Some questions to ask the breeder.

Do you have both parents. Can they both be seen. If stud not owned by breeder ask to see photo of him.
Can you see all the litter.
How old are the parents.
How many litters has the mum had.
If there any health issues with the breed. If so, ask if they need to be tested. If the answer to this is yes. Ask to see the relevent certs for both parents ensuring they are up to date.
Are they KC registered.
Dependant on age of puppy -will they have or have they had any vaccinations (first one usely given at 8wks. Second one at 10wks). Some breeders arrange for their puppies to have their first vaccinations before going to their new homes.