most PT's in the gym (and all in most franchise gyms) have no clue how to perform compound lifts. all you need to do is read a book and pass a test and boom you are certified.
also most people in gyms have piss poor form, especially on lifts like squat and deadlift.. so it is hard to learn to do it right. my advice is find that rare person who knows what they are doing and start off with low weights