Trainers should never use electronic aids like shock collars which will hurt your dog and can damage your bond with him.
Rubbing your dog's nose in an "accident" will never work and will only confuse your dog. This method is harmful, unnecessary, unsanitary, and shows your dog that you do things to him that are scary and unpleasant.
Screaming is not training.
While a confident tone of voice is helpful, yelling may work against you by instilling fear in the dog. Dogs will learn better when they feel safe and secure. Screaming takes that feeling away.
If your dog is afraid of a trainer, you should be too. A dog who is not normally fearful should not be cowering or whimpering around a trainer. If your dog is not comfortable, the training will not be successful and you should stop the session immediately.
Never let a trainer dominate you or your dog. People who try to physically dominate their dogs may get bitten. Trainers should never sit on, kneel on, or otherwise force your dog onto his back. Do not let anyone talk you into doing this. Your dog may try to bite or could get seriously injured from this process.
Choking is not training. Always avoid the use of choke-type collars and trainers who would lift a dog off of the ground by his collar. Recent scientific studies show that choke collars cause injury. Even if the trainer uses a regular collar or harness, they should never yank your dog around on the leash.
"Don't worry, he's fine," is something a trainer should not have to say if they have explained what to expect out of their training methods, Like a head halter some dogs may rub & roll on the ground etc... to get it off there head this would be explained before it goes on. If your trainer is constantly reassuring you that their methods are safe, it's time to look for another trainer. Training techniques should always appear safe without reassurances.
Physical violence is unacceptable. This may seem obvious, but never let a trainer hit or kick your dog. Such methods are ineffective, dangerous, and possibly illegal. Training should never be abusive.
Bleeding is bad. Your dog should never bleed, vomit, or foam at the mouth as the result of a training session. If any of these things occur, contact your veterinarian immediately. Injuries should not be a part of a training session.
Trust your instincts. If you are ever concerned or uncomfortable with anything that your trainer is doing to your dog, end the session. Your dog depends on you to keep him safe, and you have an obligation to speak up to protect him.