The strap usage at some gyms is getting out of hand. When I was at the local YMCA I saw guys curling with straps. Yesterday I saw a guy rip a 810 DL with HOOK grip... between that and mixed, one probably would never need to use straps.
To get the trainer off your back, just say you are training for a PLing competition and straps aren't allowed... that should shut him up! :-)