No, it is really not hard to see a person face most of the time, people sweat, remove their balaclavas and face masks all the time.  Besides, i may not catch the offender the first time but its my experience that most people are creatures of habit, so if you are out in my area odds are, that person will be out there again. Hunters are patient people and gather data all year long. Good to know whats in the area before you start trapping there.