No, you don't get commission. The hours are pretty long I will tell you that. I wasn't a fitness instructor (nights in the crew bar killed any hopes of any type of fitness) but I did know the steiner girls (as most did) the instructors didn't work as much as the salon girls though and unless it's changed, they do some of the cruise staff things like hanging out in the disco to encourage dancing, where other staff are not allowed to go. It is long hours, not the best of pay, you're on the ship for 6-9 months at a time, but you do get to see a few different ports and you will make the best and closest friendships. If you don't mind sharing a little cabin with another girl, then go for it, It's an experience.