Questions to ask the breeder.

Age and cause of death of 5 recent generations. If they mention cancer, ask for the type. Some such as osteosarcoma are genetic. Of the deaths are under 8, it may run very high in the line.
Age and cause of death of siblings in 5 generations.
Ask to see test results. Not just take there word. When was a heart echo and holter done. If parents are under 5 years ask for results on grandparents. * You want to see hips, eye, thyroid, liver panel, Von Willebrands (vWD), heart echo and holter*
Ask for the contact information on previous litters from same parent. If first litter, as for info on parents' siblings.
Do they breed fawns and/or blues?
The size of the dogs breed. The Doberman is a medium size breed. They should nor exceed 28 inches tall nor 90lb. 100lb+ warlocks should be avoided!
What was your goal in choosing this breeding pair and having this litter? This question is important as some breeders are in it for the money. They have no interest in improving the breed.
How many Champions have their bred? Are the litters parents Champions? What success do they have in conformation, obedience, or sport

---- If above is good ---

What titles do the parents hold. What titles do previous litter mates hold.
How are the puppies weaned? Many breeders wean too early to get the bitch back in show or trails. Some may wean to late allowing the puppies to have teeth and not properly associate with food.
How are the puppies socialized? You want to here they are socialized individually away from the security of there pack.
How do the do there temperament test to choose the right dog for the owner?
Are the ears, tail, and declaws done? If so what age, what vet?
Is the litter going to be registered?
They should have just as many questions for you!
Read the contract. You want one to protect you, not just rants to protect them.
Can you keep the dog intacted?
What do the consider genetic health problems? Do you need to return the dog if one develops in the time line of the health guarantee? Are you offered another dog from a different line or you the price paid without returning the dog?

Remember you are interviewing them, don't feel it's you who is up for the approved home test. Your not rescuing a dog from a breeder, if they are a bad breeder you are supporting their actions and they will breed again. A good breeder and bloodline is hard to fine, but they are out there!