Pros
I was at a franchise one, and the manager there was one of the reasons why I was influenced to be such a great sales consultant. He was wise beyond his age and taught me strategies of how to sell products by accommodating with each individual to keep coming back. Yes the incentives for certain products were commission-based, but it's a rewarding experience seeing people come up to you, knowing you had a part in their lifestyle change/goal achievements. Very flexible and even if I worked all day, I still get out at 8/9pm depending on which location I was put at. The location also had great customers so that should definitely be a consideration if you were to work at a GNC.
Cons
Because I am a girl, there was a lot of judgment and doubt about how well I know a supplement or what they're trying to achieve between specific customers but I was able to convert ignorance and stubbornness through confidently stating facts and advice. There is definitely dead times throughout the day, but there should always be something to work on depending who you work under. Never really a rush but if there is, it may be overwhelming if you're new and alone.