Is it Really the Dog?

There are times the dogs come back with a story behind them... "This dog is not housbroken. It poops/pees in the house everyday". I then take the dog back wondering why the heck he/she is acting this way b/c the while in the foster home it never had an accident. I then get the dog back and it never has an accident. I start to wonder was the person telling the truth? Was the person not taking the dog out? Was the person leaving the dog alone for too many hours? You really have to wonder why the heck the dog would be perfect in the foster home bad in the adopters home and then fine after it was returned. Then you have the people that say the dog is aggressive or in some case the dog did bite. And this is behavior that you never expected from the dog. I then get these stories from the people on how the dog is aggressive towards the kids and she just doesn't understand why. The dog has been fine and the kids are always wrestling and playing with the dog. I get the dog back and he is 100% fine. You can do anything to him and I have him around kids and nothing. So was the person telling the truth or did the kids do something to the dog that made him fearful of them?