Breeding is their main source of income, money may be more important than a good client relationship. May indiscriminately go to the winners for breeding to ensure sales. May send their dogs to professional trainers, thus do not know the training idiosyncrasies of their dogs. Puppy Mills fall into this category. So, the main thing would be to find a breeder you are comfortable with.
Many hobby breeders give a wealth of support to their buyers, as do professional breeders.
Hope this helps you weed through the ads and websites. Once you get the perfect pupster, it is up to you to finish the work.