It is possible there was some abuse issues, but GSD's are actually quite sensitive dogs and do not react well to yelling or physical punishments. Positive training works exceptionally well with them.
It is far better for the dog to learn that if he does something "bad" then something he likes gets taken away. Example: Dog pees on rug in front of you. You yell NO, rub his nose in it & toss him outside. Dog makes connection that peeing where you see it is bad, so next time he pees in your shoe!
Now: dog pees in front of you, say nothing, quickly take dog to his outside pee spot & wait. As soon as he pees celebrate & treat. Dog now knows peeing here gets me something good. I think I'll do it again!
OR: dog jumps on you, turn your back & ignore him. Dog learns I jump & I lose valuable attention. I won't jump again.
