My problem with trainers that I've seen is they try to get people to move a ton of weight with poor form. I guess it's easier to convince someone your program is working if you have them doing 400# half squats instead of forcing them to do about a third of that with safe, proper form.
It gets really bad with women. I saw a trainer put a tiny woman, who had obviously never squatted, under 135 lbs. He also put a box behind her. She was shaking and telling him there was no chance, yet he persisted. She managed to bend her knees slightly and he had to help her lower the bar onto the pins, which was nearly impossible given the box. It was appalling, and I'm sure she was injured.
It's probably better at better gyms, but even some of the crossfit promo videos have parts where they're making women do things that are just
Off topic I guess, but I just had to air that.