
Have they proved their bitches worth in some way appropriate to the breed, compared her to the breed standard by showing, or worked the bitch.
Has the bitch had all the recommended health tests for her breed, and are you pretty familiar with the dogs behind her, as to whether combining with your dogs liens is likely to produce quality puppies.
Of course it goes without saying that your boy should be likewise.
Then do they understand the lifetime commitment to the puppies they may produce and be willing to take back or make provision for these pups, are you willing to do this too as the stud dog owner?
Have they the knowledge to properly rear and home a litter of puppies and offer the knowledgeable back up to new owners?