Well, to be fair, it isn’t hard to get certified as a personal trainer, and most PT’s are complete idiots and don’t know how to do proper exercises. I could tell you some stories about methods of PT’s that would blow your mind. Many Gym rats read quite a few articles and spend quite a bit of time researching physiomechanics and probably know quite a bit more than some smuck trainer with 13" arms and a penchant for running on a hamster wheel.
I admit, though, that there are still quite a few gym rats that only read bodybuilding magazines and have just as silly concepts of what it takes to get in shape.