If you buy a GSD pup, expect the same as if they were in the wild. They sort out who is the alpha as they grow. If they nip an ear of an adult, they get snapped - hard. For us, we play like normal and expect some blood from those little needle teeth. But we correct them when they seem to be a little overly zealous about it. They quickly learn they can play but you are still the alpha. If you want a GSD that respects you then you need to be the alpha and if you have children they need to be higher on the totem. Never growl at family, never play bite with children, if they get too rough grab them by the scruff and shake them with a loud correction. Fail to do this and you may have an alpha and the family will be subordinate. If they are a strong alpha, they may end up challenging you later. They are very loyal but they respect a pack hierarchy.
GSD's are IMO the greatest dogs on the planet but training them is all with discretion and common sense. You can also end up making a pup fear you and that is not good. Most US lines are not aggressive but some European lines are. There is a segment of people that think it is cool to own a GSD but don't have the temperament themselves or have a clue how to raise them - and should not be GSD owners. They are not neat pets - they are part of your family, your "pack".