unless starting from scratch youself , i,e if you want a bull greyhound , breeding your own from pure bull to pure greyhound ect , you will never know really whats in your dog , you just have to rely on the honesty of people , problem is , this day and age people will say out to sell on something , for instance a dog that actually starts of as been 3/4 greyhound 1/4 bull , after been passed ona few times ends up been bull greyhound x collie greyhound ect , then your breeding it with another dog , which also may be the reality , that its a true unknown breeding , just what people have told you