As part of your screening process, ask to see a copy of the breeder's contract and health guarantee. That is also the time to ask to see pedigrees of the parents and to make sure they are registered with the AKC (not one of the many alternative "paper" registries).
You should also ask what health testing the parents have had. Some breeders will try to pass off yearly physicals and vaccinations as health testing, but don't be fooled. The parents should have had bile acids tests to make sure they are free of liver disease (Yorkies are 36 times more likely to have a liver shunt than all other breeds combined), xrays of knees to check for luxating patellas, eye exams and a thyroid panel. Ask to see documentation that these tests have been done.
Here is a good example of a contract from a reputable breeder. Notice that genetic conditions are covered for five years, that the breeder must be contacted if for any reason you can't keep the puppy
over its lifetime and that it includes a spay/neuter clause.
Foxstone Maltese Pet Contract