Your dog's life is in your hands.
The term "trainer" implies some degree of knowledge with regard to a specific activity. Being a trainer does not mean that you are an expert; nor does it mean that what you teach is useful or pertinent. As far as being a dog trainer, there is a vast degree of difference in those who call themselves a trainer. I met one girl who said she was a dog trainer; when we started discussing behaviors it was obvious that she didn't understand what I was talking about. She did not have a dog of her own and had only been training at PetSmart for over a month. Scary. She was teaching people how to train their dogs.
There are trainers and there are trainers with experience. Experience teaches you more than anything in a book; hands on work with dogs is real life experience. Each dog is different, working with a new dog always comes with new lessons. There have been times when I was really surprised by a displayed behavior; a new lesson was learned. Truly understanding dog behavior means that you can never assume that something will work. You must have alternative tactics for when it doesn't work.
Working with dogs is a never ending lesson. Those who think that it is done one way and that is how you do it, is not someone you want training your dog. Typically conventional choke collar trainers do it one way; that is where the collar comes in. Take the collar off, the leash off and where are they? They are stuck with no means to teach, sad. If they cannot yank a dog around on a leash and collar they really have no knowledge of how to interact and teach the dog. Everyone should take collars off and see how much real control that they have with their dog. If you cannot rely on a collar for control; have you got any sort of control?
My training is geared around living with extremely well behaved dogs. I do not teach agility, flyball or other activity type training. I know many dogs who are amazingly well trained in their field of competition but off the field they are literally a fur monster on four legs. This is a major reason why I love doing in-home private training; I get to see the dog in the home where the action happens. Each dog's training is set up for that particular dog in their home with their people.
In the world of training there are the inexperienced newbies, trainers stuck in their ways of the past, those who only know one way and the very harsh unbelievable trainers. It always surprises me how many harsh trainers are still around and that people allow these trainers to do what they do to their dogs. I have heard of one trainer who comes to your home and immediately alpha rolls the dogs. People stand back and let it happen. One woman I talked to told me that her dog bit the trainer pretty badly after being alpha rolled; not surprising.
Over the years I have undone a great deal of damage done by inexperienced or harsh trainers. When I meet the owner and hear about what the trainer did to their dog, it makes me mad. I explain to the owner what has happened to their dog and then we get to fixing the issue. Many bad trainers use bullying tactics to sell their talents. They use the owners feeling of inexperience to fuel the "you're going to wreck your dog," idea. I have heard this time and time again from owners who put blind faith in a trainer and now live with the guilt.
When you hire a trainer, no matter what trainer that is; you must feel good about what they are doing or asking you to do with your dog. If you shudder at something your trainer is doing to your dog; don't do it. Not everyone has you or your dog's best interest at heart. Inexperience, greed and anger have no place in dog training. Much damage can be done by a trainer who lacks basic knowledge about canine behavior.
If you feel the least bit apprehensive about a trainer, find another. Your dog is worth the best.