Be selective when choosing the breeder. Ascertain that he breeds in accordance with guidelines set forth by the VDH, or, in countries other than Germany, the FCI (Fédération Cynologique Internationale). 

Prior to the purchase of your puppy, meet the breeder and his place of breeding - even if it requires extensive travel; this will pay off in the long run. Inquire about the test results and assure that the dogs are being kept in an adequate environment. Ask about the puppies interactions and what is being done for their social environment. 

When dealing with a foreign breeder ascertain if the puppy's parents have been tested x-rayed for HD (hip joint dysplasia), ED (elbow dysplasia) and if their eyes have been examined. 
These procedures are not necessarily required in countries other than Germany. Prior to breeding, a responsible breeder will always subject his dogs to these examinations

Another issue to watch for is how many dogs the breeder is keeping. If, for instance a breeder is owner of about 20 dogs, the question arises - even for the layman - whether or not these animals can be kept in acceptable conditions, especially receiving adequate training and exercise. 

As a rule, the potential buyer will be required, by the breeder, at least one visit to his home, prior to the birth of the puppies to ensure the potential owner is suitable. 

Extreme care must be exercised when dealings for the placing or purchase of a puppy are being conducted and finalized over the phone. Being aware of the extensive waiting periods, it is always very difficult to reject a puppy. In these cases the head, not the heart should always decide.