Research research research research and did I mention RESEARCH?
Honestly, I would recommend a shelter or rescue dog, with pibbs a lot of them will have puppies. The workers will also be able to tell you which ones seem to get along better with their other animal companions than others.
If you need a breeder... Look for someone who only works with ONE breed. Multi-breeders are a hallmark of BYBs. MAKE SURE they will let you see and interact WITH THE ACTUAL PARENTS. Keeping mom and dad locked away is another hallmark of a BYB. Talk to the breeder, do they seem to know what they are talking about. Do they crop all their dogs ears? (not always an indicator, but if you're on the edge about purchasing) Are their dogs ears cropped professionally? Or does it look like the pup got a hackjob with some garden sheers? Are the dogs friendly and well socialized? Are they participating in any CGD --canine good citizen, are they registered. Do they do health testing with the parents before breeding. Ask about what veterinary care the pups receive. Are they active with any pit rescues in the area? Do they have a mandatory spay/nuder clause for any pet-home puppies? Do they SHOW their animals?
Also, avoid the pits that look like they have taken steroids..
I think thats all i can pull out of my brain for now.
Also, those don't just apply to pit breeders, they apply to ALL dog and cat breeders.