I wouldn't say it is impossible. If you have a company that are ready to hire you, and that company has a few people employed. Then you "might" be able to get it to work. Yes, at least you need to pay taxes on a 50k or 60k salary (depending on where you are from) and registered capital for the gym might be an issue. But also remember that in Thailand things are not that black and white. I can tell you as much that you need professional help with this (there are plenty of companies with the right expertise, some more legit than others). If you can't get a work permit I am very sure there are tons of other options for getting a visa. A general advice would be that whatever you do, this will not cost you much, if someone claims that it does, it is a scam.