When going overseas always ask yourself "would I do this back home?", would you take the risk to work on a tourist visa in your home country, especially if it's the US or some European Union member knowing that illegals get jailed and deported at their own expense there? I doubt you would, so why doing it in China?

Simple answer: coz there's STILL no rule of law in China. I say so from my previously lengthy and currently ongoing employment experiences in that regard.
BTW, what's a personal training centre? Is that a live example of yor dodgy English, or that of a Chinese director's Chinglish of said joke of a chain school?