
I wouod always go for a breeer who was a member of theri breed club/society. This would tell me at the very least that they ahve more than a casual interest in theri breed and to some extent will be bound by the clubs codes of ethics and rules.
Club secretaries can advise what the doen thing in theri breed is regarding health testing, age of homing pups, likely price, and will ahve the names of breeders that have or are planning litters. A breeder worth the name will ahve no objection to you asking for references, and perhaps put you in touch with puppy buyers in your area so that you can visit if they will allow.
A breeder belonging to their breed club will also want to keep a good reputation among their peers.