Your success will depend on one thing and one thing alone = your sales skills.
You can be the best trainer or the worst, nobody will really care. Ultimately it will come down to SALES. If you have the balls and the skill (that is SALES) then I say, go for it. But don't expect to hardly be able to eek out a living.
If you are going to work for a gym. They will get all the clients' money up front and pay you a flat hourly rate based on how many times you train that client. If you don't make your quota - you get shitcanned and the next dope will inherit YOUR clients and that person will get the flat hourly rate.
Good luck if you want to work for yourself. Insurance, gas money, equipment investment are all things you need to consider if you are going to be traveling to train clients in their homes.
I did it for about 2 years and though there was a certain level of satisfaction when I helped out A LOT of very different clients with very different goals/needs in the end I wasn't paid nearly enough. Even my young girls (we are talking ages 8 through 12) recognized that when they would see how hard I would work with my clients and all the research I did when I was not with the clients (gym had a childcare).