“Forcing the dog onto its back is the equivalent of an abusive parent beating a child to force it to say, ‘I love you.’  Although he or she may have forced the words out of the child’s mouth, they cannot force the statement to be true…. Forcing a dog into a submissive position is the Doggish equivalent of this scenario.  Even worse, this technique may actually anger the dog enough to provoke it to attack.
“Forcing a dog into an alpha roll, or shaking the dog, both constitute physical aggression.  Physical aggression is not communication.  If there is good communication, then such confrontations need not occur.”  - Stanley Coren, “How to Speak Dog”

This is why we support POSITIVE REINFORCEMENT dog training ONLY.

If a dog tries to do what you want the dog to do out of fear only, you will NOT have a happy, well adjusted dog.  Your dog should WANT to mind you (and will with Positive Reinforcement training).
If your dog appears to be afraid of your trainer, do NOT continue with him/her………because, YES, the dog truly is AFRAID, there is a difference in respecting a trainer and fearing him/her, make sure you are reading your dog’s behavior correctly!!