Don't quit your day job
The worst part is working for a chain such as Bally's or 24H Fitness. They want you to sell,sell,sell! I understand that it is part of the business but they take it a little overboard.
The quality of the training is not there sometimes because it isn't how many people you help it is how many people you sell training or memberships to. They could care less if they have results as long as they sell something and exceed the bottom line. I know there are exceptions but walk into any franchise gym and you will find this is true.
I also want to warn anybody about starting a personal training job at one of these fitness centers. Don't quit your day job. I made this mistake and couldn't hack it because my sales were weak and even if you are a good salesperson it takes months or years to build up a dependable clientele. I would recommend starting part-time to see how you like it. I also think it is good to get experience as a trainer at commercial gym so you can learn more while collecting a paycheck.
Last but not least I think that working at a commercial gym can be beneficial because it teaches humility and you will always have that experience to remind you why you went into business for yourself or why you quit being a trainer!