Don't assume that since someone looks really good that they know anything other than how to train themselves. This shows that they have a certain degree of knowledge and competency for personal training. Ask about their background and experience. You really do not want anybody experimenting on you. Be wary of trainers that are certified by health clubs.
Many health clubs have four day seminars where anybody who can study can pass their exam.
Trainers at these clubs may have had no further experience and have no practical knowledge. Just check to see if they have any other credentials or experience. Well, if you don't know if you are working out correctly, think you maybe spending way too much time in the gym and not seeing any results, can not seem to even get to the gym, look into getting a Certified Personal Trainer.