There are many different types of breeders out there. The only thing standing between you and an unscrupulous breeder is your knowledge. That's it. But how can you tell the good from the bad - or the ugly?
Please note - simply because a breeder misses out on one or two qualities of a "good breeder" does not make them a "bad breeder" - hence the term "questionable." There are exceptions to EVERY "rule" and it is expected that the buyer will have the common sense to know the difference between "justifiable exception" and shoddy breeding.
This list was compiled based on the reading of no fewer than a dozen books on many breeds of dog, speaking to countless breeders, membership on several dog-specific mailing list, and furthermore is not specific to Corgis alone, can be used for just about any type of purebred dog a person is interested in acquiring, and is as unbiased as is humanly possible, though it may seem otherwise at times. If you have any questions about this article, go to an impartial third source - a trusted vet, a breeder you don't plan to buy from, the director of your local humane society, etc. - and ask them for a second opinion.
Due to the length of this article, you may want to print it and read it later... or in stages.

GOOD BREEDERS know and love one breed, more or less, to the exclusion of virtually all others. Sure, they may own other breeds as pets... or handle them in the show rings, if they are also handlers... but MOST good breeders do not raise more than one or two different breeds. Good breeders also may not have a litter ready for immediate purchase - in fact, they probably DON'T - or have a waiting list. This is typical... the best breeders, because of the extreme amounts of time and money involved in raising a litter properly, will often breed only one or two litters a year. Ask your breeder what goes into raising a litter - the midnight whelpings, the bottle feeding of weak pups, the rushed trip to the vet to nurse a pup who isn't thriving - and you'll understand why most breeders simply don't have the ENERGY to raise more than two litters a year! A good breeder can and will, however, help you find a breeder who does have a litter.
Good breeders can also provide you references, if you ask for them - the names of people who currently own pups from previous litters. Always ask - and then call the references to see how happy these owners are with the pup and the breeder. You won't be sorry.
QUESTIONABLE BREEDERS claim to "specialize" in several different breeds. While it IS possible to raise and show more than one breed, this is NOT the norm, and should bring up some questions in your mind. If the breeder claims to be able to get you just about any breed you ask for... or any COLOR you ask for... or a pup as soon as your check clears... this should set off your early warning system; they may not be a breeder, but are instead "dog brokers."
Questionable breeders cannot, or will not, provide you with personal references. At this point, ask about them on a breed-specific mailing list, at your local animal protection or welfare organziation, or contact the breed club's corresponding secretary and ask what they know about this person - IF you're still willing to buy from them. And that's a big IF.

GOOD BREEDERS belong to their breed's AKC affiliated club. There ARE exceptions to this... people who breed WORKING stock as opposed to SHOWING dogs will sometimes shun the AKC as being "too foo foo," claiming that show breeders breed for looks as opposed to soundness. This may be true in some cases - this is addressed later - but the BEST working breeders still belong to other professional organizations... many AKC affiliated... and you are able to see if they are members in good standing by simply checking with the club itself (most have Web sites). The other exceptions lie in "rare" breeds, but as these have their own club affiliations (the UKC and the ARBA), there is really no excuse for a good, professional breeder not to have SOME sort of club membership to their kennel name.
Do you need to buy from a "fancy show breeder?" Of course not. Many breeders DO show their dogs in "conformation" - doggy beauty contests - but this is simply because it is the most visible purebred "sport." The very best breeders are also deeply involved in many aspects of their breed - rescue, non-conformation events (for Corgis, this may include tracking, agility, obedience, or herding), or pet-assisted therapy. Some choose not to show much in the conformation ring, being more interested in their dog's abilities rather than appearance. They will have titled some of their dogs (a "title" is the letters that precede and follow a dog's name - you can find a list of them at the PWCCA site or the AKC homepage) and are proud to say that their dogs are highly versatile. They do not, however, claim that titles or pedigree alone makes a sound dog... anyone who expects you to be blindly impressed by pedigree, titles, or trophies may be hoping you don't see past the glitz.
QUESTIONABLE BREEDERS do not belong to any organizations... or are members in poor standing. While the "sport" of purebred dogs can indeed be a nasty, backbiting society at its very worst, with rumor and treachery present under the surface (sounds a lot like a soap opera, doesn't it? <g>), this dark underbelly can be avoided... and often is... by true sportsmen and women who are in the sport for more than mere competition and glory. A breeder that claims that they avoid organizations simply due to the unseemly side of things may be honest - or may be hiding something. You can't rule out a person based on organizational membership alone... but keep your eyes open for other signs of concern.

GOOD BREEDERS breed for "the whole dog" - not for one particular aspect of the breed. The best of breeders want to show off their prized babies in all lights... not simply as being the prettiest pooch at Westminster. While an active show dog does not have much spare time to give to obedience, agility, or herding, the breeder is certain to have retired dogs working towards titles in these other areas. Similarly, while each breeder has particular goals for their pedigrees - the "look" that sets their dogs apart from the competition - those who focus on one trait to the exclusion of all others may not be as well-versed in the breed as they would like you to think.
QUESTIONABLE BREEDERS focus on one trait or ability alone, breeding "giant size," "exceptional working ability," or "long, fluffy coat." Beware of exaggerated physical traits like size, length, or coat. Beware also of "ability" at the expense of temperament. If the advertisement focuses on catchy words rather than on health certifications and club membership, pass it by.

GOOD BREEDERS generally have a profession outside of breeding - or have had one that has set them up to pursue breeding in their retirement. Good breeders run boarding kennels, training facilities, and work "people jobs." Breeding and showing dogs is expensive - don't let ANYONE tell you differently - and it is the truly rare breeder who can devote all of her time and energy to her dogs. If the breeder runs a dog-oriented business, ask for client references... find out how this person is viewed as a business owner as well as a breeder. This will give you a well-rounded view of the person, as well as the breeder. If you wouldn't board your dog at her kennel or let him train your dog, don't buy a pup from this person.
QUESTIONABLE BREEDERS "make money" on their dogs. Most breeders, when asked if they "make money" on their dogs, will collapse laughing and wheezing on the floor, tears streaming from their eyes. Between medical expenses, stud fees, show fees, training classes, grooming, and many other supplies, most breeders break even on a litter of pups... if any profit is made, it is slim, and is usually put straight back into the dogs. A breeder that claims to support themselves by breeding is likely breeding for quantity, not quality, and should be avoided. Worse still is the breeder who tries to sell you a pup telling you that you can breed her and make back your money... run, do not walk, away from that place!

GOOD BREEDERS love their dogs like family members and make sure they are well socialized pets first, show dogs second. While some of the "big name" breeders have private facilities where dogs are kept in heated kennels when they aren't out showing, many others keep their dogs in the house with them... they wouldn't dream of having it any other way! Their dogs are fed the best of foods, played with, allowed to sleep on the sofa or in the family bed (sometimes!), and taken for long walks where they meet many other people and dogs. "Pet quality" puppies - those not destined for shows - are given special care in the socialization department, so that they meet many, many other people, dogs, and situations before ever setting foot inside their new homes.
"Socialization" means that a puppy is introduced to new things slowly and carefully so that these will not frighten the pup later in life. A pup who has never seen a car driving down the road will likely be terrified of it! Additionally, all young puppies go through a "fear stage," when it is perfectly natural to fear strange new things... the best breeders will have taken care to assure that the pups were carefully nursed through this, as fearful experiences during these vulnerable periods can result in a dog who has a lifelong fear of strangers, large dogs, cars, loud noises, etc. A pup who has not been properly socialized is a pup who WILL have problems down the road. No professional breeder who knows their breed will leave socialization entirely in the hands of the new owner... by then, it may be too late. By the time a pup is a year old, he or she should have met a MINIMUM of 100 people of many varying ages, races, and sizes... and many other dogs as well! The best breeders will give you careful instructions in socialization so that you can help your pup adjust to his or her new home.
QUESTIONABLE BREEDERS raise dogs only in outside kennels that may or may not be heated. The dogs are rarely, if ever, taken into the house, on walks outside the breeding facility, or for rides in the car. They play only in "dog pens" or "exercise yards." Beware - the breeder WILL have very logical-sounding reasons for this... anything from "it's unhealthy to take them outside too early" (yes, but what about after they're old enough? And what about vaccinations?) to "the dog needs to be used to YOUR house, not accustomed to mine; they'll be homesick if they get used to me." Uh-huh. A questionable breeder will brush aside a pup's fears - "she'll grow out of it," "they all go through that," etc. - and provide little guidance in helping your puppy adjust. When asked, "how were these pups socialized?" a questionable breeder will be confused by the question, or evasive. NEVER buy an unsocialized pup for any reason. Fearful pups often grow into "fear biters" and dogs with severe emotional problems, and are unsuited for first-time owners. (This includes a pup who has spent its formative weeks inside a pet store cage. While these pups have indeed been exposed to a wide range of people and other puppies, they have no knowledge of the world outside... a heavy blow to overcome.)

GOOD BREEDERS VACCINATE THEIR PUPPIES!!!!!! There is no need to explain this. Even pet stores vaccinate puppies, and that's saying a lot. Do NOT buy from a breeder who does not vaccinate. Ever. While the chances of your pup actually contracting an illness is not great in many circumstances and with caution, it's a minimal expense and a chance most folks don't want to take.
QUESTIONABLE BREEDERS do not vaccinate their puppies, and have every excuse in the book for not doing so. They will speak knowledgeably of the immunity that a puppy gets from its mother (this lasts until the puppy is weaned and diminishes daily from that point) and try to instill fear into you when you question this - speaking of "scientific research" that indicates that pups who are vaccinated too early are at risk for disease, including cancer. They claim that vets cost too much money (note - most breeders don't make money on their litters, and many know that they are well able to administer vaccinations themselves for a fraction of the cost of a vet). If the breeder is truly a professional, they will know both WHEN to vaccinate and HOW to vaccinate. What would you say to a person who refused to vaccinate their children?
The only feasible exception to this rule is a breeder who does not vaccinate either children or puppies on religious grounds... at which point, it's an ethical choice only you, the buyer, can make.

GOOD BREEDERS are very willing to talk to you about breed-specific health problems, and will provide evidence of proper testing in the pup's mother and father. ALL purebred dogs - and many mixed breeds - are susceptible to a variety of hereditary genetic diseases... hip dysplasia, various eye conditions, elbow problems, deafness. A glance in any good multi-breed book will tell you what diseases your breed is prone to... and the best breeders test ALL their dogs BEFORE breeding to assure that they do not pass on these diseases to their offspring. They will provide certification and explain it without being asked... or, if they don't, will gladly produce and explain it at your prompting. The best breeders know their breed's strengths as well as its weaknesses.
QUESTIONABLE BREEDERS do not test their dogs for hereditary conditions, or are unable to provide proof of testing or explain the test results to you. Many will claim, "MY dogs don't have THOSE problems." That's wonderful - how did they manage that, when the breed as a whole has been unable to rid itself of the problem? They will blame vets for not doing the testing right, the AKC for promoting costly tests that put an unfair burden on "regular everyday breeders," or claim that a good breeder doesn't need to worry about genetics. Any way they put it, it's an excuse... and a poor one. Insist on testing. Your wallet will thank you for it later.

GOOD BREEDERS can provide and explain the pedigree of your puppy's mother (and possibly father), including all titles, and will explain what sort of registration you can gain for your pup. A good breeder is happy to explain what "ROM" and "UDX" and the rest of the alphabet soup that follows a truly outstanding dog's name. They will explain to you why certain dogs have "Ch." in front of their name - and why a pedigree of champions alone does not necessarily indicate highest quality. Similarly, while it's very nice to have a pup of champion parents, understand that your breeder may still be working the mother to that goal... Riley's mom got her Canadian championship first, and her American championship after he was born! Similarly, the breeder will explain to you what "registration" means, if you can register the pup you are purchasing, and under what conditions.
QUESTIONABLE BREEDERS either have no pedigree to offer you, cannot (or will not) explain a pedigree that they DO have, or hope you will be impressed by all the "Ch." prefixes, and ignore that no titles FOLLOW the names of most of your pup's ancestors. In the case of pedigree, saying too much about champion status can be as bad as saying too little. If, however, the pedigree boasts NO champions with NO titles after the name of the dog, you should begin to wonder... why were none of these dogs ever shown in conformation OR in events like herding, tracking, schutzhund, or other canine sports? A bare pedigree is evidence of a less-than-enthusiastic breeder.

GOOD BREEDERS have the puppy's mom available for meet-and-greets before and after whelping; you will know a lot about your pup's temperament by interacting with her and with the other kennel dogs.
QUESTIONABLE BREEDERS don't want you to meet the mother, or brush off her personality flaws. If the breeder doesn't even OWN the mother, you really need to ask some questions about WHY.

GOOD BREEDERS have happy, clean dogs and clean, safe facilities with plenty of doggy toys about the place. Even if the breeder keeps her dogs in a kennel when they aren't in the house, you will see evidence of house dogs around... fenced yards, toys, bowls, teeth marks on the walls and furniture... <g> If you don't feel comfortable in the house or kennel, make note of that and try to figure out why.
QUESTIONABLE BREEDERS have facilities that make you wonder. Excessive odor, dirty kennels, dirty dogs, dogs who seem fearful or listless, lack of toys or proper bedding... think about all the doggy supplies you intend to buy your pup. If these aren't present, move along... you'll find another breeder who spoils her pups rotten, and a spoiled pup is likely to be a happier pup than a neglected one!]

GOOD BREEDERS will give you the third degree before offering you a pup. You need to expect this. A good breeder will NEVER sell to a pet store, simply because he wants to know EXACTLY where the puppies are after they grow up. They will ask you many, many questions - some of which may seem invasive: Where will the dog sleep? What kind of hours do you work? Can I meet your children to be sure they know how to behave around dogs? Who will be primarily responsible for taking care of the dog? Are you willing to fence your yard, if it is not already fenced? No, not electric fencing... I sell only to real, solid fenced yards.
And the list goes on. The more questions, the better - unless you head them off at the pass by presenting your list of qualifications for owning a pup first, and follow it up with questions of your own! A good breeder will never be offended by your questions, so long as they are well-founded, thoughtful, and politely phrased. A good breeder WILL grill you, but they will NEVER put on airs to make you feel unworthy of a pup. A good rule of thumb: Never buy a pup from a person you wouldn't be willing to go out to dinner with. Your relationship with your breeder WILL be long-term. Best be comfortable with the person as well as the pup!
QUESTIONABLE BREEDERS simply state the price and ask no questions. At the other end of the scale, they may make you feel like you are LUCKY to get one of their pups... that you may not deserve it, but they'll do you the honor of allowing you to purchase from them, if you don't ask too many questions. This is not the relationship you want from your breeder. Look elsewhere. People in it for the money may not be there when your pup is sick and you need advice. A good breeder is someone who will call YOU to see how the pup is doing, and will be thrilled to receive Christmas cards each year!

GOOD BREEDERS PUT EVERYTHING IN WRITING. They will require you to sign a contract stating the terms of sale, and will provide you information on vaccinations, medical history, feeding schedules, and often many, many other bits and pieces that will help you and your pup get off to a good start. They will have in writing that they will take back the pup for any reason if the relationship doesn't work out, and will probably require you to spay or neuter your pup if you aren't purchasing a show quality pup. Many will require a deposit that will only be returned after the pup has been neutered. EVERYTHING about the pup and its history will be provided to you in writing, to be kept in your files - including a written guarantee of health and behavioral soundness.
QUESTIONABLE BREEDERS put as little in writing as is humanly possible, don't require neutering or spaying, and may or may not have written medical guarantees on health, soundness, and temperament.