A GSD can have weak nerves without having been mistreated. It is possibly why he was turned into the shelter, because he didn't 'act like a German Shepherd should'. Just a guess, could be way off base.
The best thing to do for an easily frightened dog is to expose them (SAFELY) to as many people, dogs and situations as possible. Again, safely. Be patient but persistent. Do it gradually, don't throw him in over his head. But do give him daily doses of socialization. Don't be too concerned if he never becomes very friendly with other dogs, but try to get him to a point where he at least tolerates them and isn't aggressive or fearful. Best of luck, it could be a long process and you might never succeed in all areas.
Last edited by Pooky44; 03-12-2013 at 01:32 PM.