There are some very real differences. For example, jaw strength. A large German shepherd may look like a wolf, but the dog thanks to its partnership with humans hasn't had to crack open the leg bone of a moose for thousands of years. Consequently, it no longer needs the jaw power necessary to do so. A wolf, on the other hand, needs that power, and has twice the bite ability of the dog about 1,500 pounds per square inch.
Paws tell the same story.
Very few dogs, even ones as large as a wolf, need to move efficiently through snow, so their feet can be smaller. An adult wolf's paw print is about the size of a man's fist. Unlike dogs, there's a heavy furring between each toe. If you see large tracks in mud or snow, you can tell if it's a wolf or a very large dog by looking at the claw marks. A dog's claws radiate out from the paw, while the two center claws in a wolf are parallel.