If a trainer tells you to do something you don't feel good about, don't do it. Don't be intimated, bullied, or shamed into doing something that you believe is not in your dog's best interest. Avoid trainers that offer guarantees. That trainer is either ignoring or doesn't understand the complexity of animal behavior. Avoid trainers who object to using food as a training reward.
Food is an acceptable positive reinforcement training tool.
Avoid trainers who won't let you use any training collar other than a choke chain. Head collars are humane alternative to chose chains and pinch collars. If you believe your dog has been subjected to cruel treatment by a trainer, get the names and phone numbers of witnesses. Take your dog to the veterinarian immediately for a complete physical. Tell them that the results of the exam may be used as evidence in a court case so that they will document the procedures with that in mind.