There are many ways to potty train any dog, like encouraging them with the best dry dog food, positive and negative enforcement. For Pit Bulls, they are more stubborn than some other breeds, therefore the process can be quite hard.
I've seen many people rub the Pit's face into his excrement to show him that he did wrong. In this case, I think the owners are the wrong ones because it will only attach the fear and hate to you. There are much more productive methods to house train your Pit Bulls.
Accidents are inevitable, yes, therefore you should always be prepared for them. It may not make sense to you that even when you buy the best dry dog food for Pitbull for the dog, he still betrays you by pooping inside the house. But it makes perfect sense to him, he will do it when he feels like it. Excessive sniffing is a common sign of your Pit looking for a place to “release”.
If you notice the dog sniffing excessively, take him outside immediately and wait for the deed to be done. After 5 or 10 minutes and the dog still hasn't done it, then bring him back home, but keep an eye on him anyway. After all, the best way to prevent accidents is to keep your attention on him all the time until your dog learns he needs to go outside for the business.
House training should take place when the dog is still young, which is about a week when you bring the pup home and be kept up until they are old enough to be roaming freely inside the house. You should not expect the process to be easy, because the idea of house training is totally new to the dog, and they need a lot of time to learn.
Keep your cool and take the pup out regularly. Even if they won't go, they will get the idea eventually.