How many puppies are usually in a litter?
Small litters and/or singleton puppies are common for certain breeds but if they occur you need to follow up with questions about how the breeder raises these litters to limit the problems associated with tiny litters and/or singleton pups.
A breeder that tells you there are no problems with small litters or singleton pups is a liar (liar pants on fire) or willfully ignorant of dog behavior. That is unacceptable and is a “deal-breaker” of an answer.
Know the standard litter size for the breed of dog you’re looking into. If a breeder has unusually small litters you should be wary of the health of the puppies. Small litter size (when it is unusual) is a good indicator of poor breeding practices. It can indicate a dangerous level of inbreeding and/or serious nutritional and health deficiencies in the mother. These can both seriously affect the puppies.