Well, as I mentioned earlier athenian, a hypnotist can't force you to do anything that you don't want to do.
Like, a hypnotist can't turn a man gay just by saying so. If the man does indeed turn gay, then it's because it was something he subconsciously wanted or was in self-denial about, and the hypnotist just helped him be more open about it or overcome his self-denial. But if he's assured about his sexuality and absolutely never had any doubt that he was straight, then he'll more than likely break out of the trance or just brush off the hypnotist and continue being straight. A hypnotist only has as much power as you allow them.
But, a licensed hypno-therapist would never suggest for you to do anything illegal or take advantage of you.
I think the best way to describe hypno-therapy is that they nudge you into doing something you wanted to happen anyway (or bring out something that was always there in your mind, like suppressed memories). If a smoker goes to a hypno-therapist because they want to stop smoking, then the hypno-therapist just leaves suggestions and nudges the person to alter their thinking to help them stop smoking, which is what the person wanted.
Again, a hypnotism only works as much as you allow it to work.