Avoid teaching in Shenzhen, there are too many westerners there. You'll be relieved of your teaching duties fast if you disappoint your training center boss. He (or she) can find your replacement too easy there. Another thing is salaries are low there because the supply of laowai outstrips the demand for them in the EFL field.
In any case, best to give all training centers a miss. You don't want to be exploited by such lousy employers!