If you feel like a breeder is one you'd like to work with, ask for their references. References may include the breeder’s veterinarian as well as previous buyers. The fact that the breeder has kept in touch with the families who purchased or adopted a puppy from them suggests the breeder has a long-term and supportive interest in his dogs. As the buyer, you should be prepared to do what is necessary: call other breeders, call the supplied references, check lists of membership/donors, check the online health and breed registries and more to verify that what the breeder has told you is true.
Online testamonials are seen more often these days. Unfortunately, they may or may be for real. Remember that web sites are simply there to display what the breeder wants you to see - so unless you can independently verify with the people who have posted the testamonials, you should take them with a grain of salt. Ask the breeder for contact information for the individuals who posted their reports and follow up with them.
You may also wish to research all the names associated with the kennel online by Googling to see if there are any reports of negative information. Virtually every breeder can have an enemy or two, so be sure to look at the predominant trends. Don't just take the word of a single web site (even this one!).
So the last word on this is to be sure to ask for - and carefully check - your breeders references.