A good breeder will ask you alot of questions about your lifestyle, work schedule,pets you have or had before,why don't you have them now,if you have a vet lined up that is familiar with small breed dogs, why you think a yorkie is for you etc...They are not trying to be nosy they are trying to match you up with a dog that will suit you specifically. Most good breeders will personality test the pups and know which ones will do best in which homes. The puppy that runs up to greet you first is not picking you, it is probably the alpha of the litter and the most dominant/curious/outgoing. If a challenge is what you need that's fine, but it's better to let the breeder tell you which one will work best. A good breeder will also inform you of possible genetic problems (luxating patellas, collapsing trachea, portosystemic shunt,legg-perthes etc.) and have guarantees in writing against them, usually 1 yr or more. They will also have record of vaccinations/worming given/due. They will insist on limited registration and a spay/neuter contract. They will take the time to train you on the care and training of the pup and be a resource to you indefinitely. They will require you to return the dog to their care at any point in it's life that you can no longer care for it. Most will refund you payment in full for returning the pup in the same condition you got it within a limited time frame, usually a week, just in case it's not what you thought you wanted or your other pets aren't adjusting or whatever. This also gives you plenty of time to have the pup examined by your vet, which is an appt. you should make before you get the pup. The breeder will not be offended by your questions,but encourage them and welcome your visits. They will have the litter dam on site for you to see and if the sire is not available also, they should have pics and the sire owners contact info if you would like to see him. The dogs used for breeding should appear healthy, well kempt, social and good examples of the breed standard. Pedigrees should be available for your perusal. Beware any breeder using the words 'teacup', tinies etc..Toy is the only yorkshire terrier designation. Adult weight should be between 3-7lbs. Good breeders keep their dogs where they can interact with them throughout the day for proper socialization and monitoring. not out on the back 40 somewhere. Puppies would not be released to your care until they were at the very least 10 weeks old, though 12 is better. Do not buy from pet stores or brokers and multiple breeds from the same breeder is a red flag. The site
www.buyingapuppy.com had a list of helpful questions to ask a breeder before getting a dog and should cover anything I've forgotten. There may be other opinions here, this is just what I would look for and what I provide. Feel free to pm or e-mail me with questions, Good luck in your search, Stacy