I PTed a few years ago while getting through uni.
I hated it to be honest, in the UK its horrendous, you have to be a real jerk of a salesman to win people over, which was the reason i stopped. Fitness first where pulling 300quid off me a month for the privelege of working from their gyms.
And those that do hire you in commercial gyms want a glorified entertainer or companion for their workouts, they're not interested in working hard or really achieveing anything significant. When it comes to paying people always want something for nothing.
You really have to hammer people to get them on board, you'll get one person interested out of every 30 you talk to apparently.