I would recommend a book (and YouTube) over picking a random trainer from the set of all possible trainers. I know some that are way better than a book, but I've also seen plenty that don't know how to squat or deadlift, much less teach someone else. If you're at a powerlifting or Olympic lifting gym specifically, absolutely use one of the trainers from there. Crossfit too. But if you're at a typical chain gym, I would not trust most trainers.