Pros
Place to gain experience in training for someone new to the field of training. Most times they accept any certification so its a good way to start because management feeds you clients so you don't have to totally rely on yourself to sell, but once you get your experience go some place better. As with training, your clientele depends on your location. If the people who attend your gym don't have money don't expect a ton of clients. They do promote from within so if you manage to consistently sign people up for training the chance to get promoted is there and often great sales performance will move you up the ladder very quickly
Cons
Pay isn't great. You will get complaints from clients about the customer service as they have to jump through hoops to cancel sometimes. Trainers often are not taught how to sell training so they expect you to book appointments with potential clients but some club managers don't teach you how to write contracts so you getting commission off of a deal is at their discretion.