I would not have sent your dog away. The issue happens when YOU are there. How is this trainer supposed to fix this if you are not around? Also the issue sounds like it's more behavioral instead of obedience. I would take the dog back and find a behaviorist who can work WITH you on trying to fix this. Management is very important until the problem is worked out. Your dog has bite history so should always be muzzled when other people are around.
Pookie, Papillon 4/17/09
Kaiser, GSD 4/14/11