Recently some unethical China job recruiters got themselves arrested for peddling the wrong visas and fake documents to newbie foreign teachers inbound to China and now they are cooperating with China authorities in a sting operation using "M visas" as the bait.
Plain and simple... it is 100% illegal to work on an M visa in China as a foreign teacher unless an only unless your receive an original hard copy invitation letter from a CERTIFIED and SAIC REGISTERED academy of art, music, dance, or a cultural institute directly with the special Ministry of Culture chop (red seal). This does not apply to schools that are "affiliates" or "cooperators" or "endorsed by" or "associated" with one of the above. If you cannot obtain and verify the SAIC license number with the Ministry of Culture or directly with the SAIC - take a pass and avoid the grief, expense, and legal problems you will encounter AFTER you arrive in China.
Because of the difficulty of unregistered/unlicensed schools and recruiters getting the required Z work visa for their teachers, many have resorted to this M visa fraud which is getting too many teachers arrested and deported in recent days. Forget what any recruiter tells you, you will not "just get a warning if you are caught". You will go to jail and get deported with a 3-5 year reentry ban and blacklisted from ever working in China again in any profession. See: http://www.scam.com/showthread.php?t=620155Plain