I did a lot of homework on this topic at
https://reddit.com/r/cftu and found the below which makes it very easy to spot a fake or shady, or illegal employer in China. If they cannot send you a high-resolution color scan of their SAIC business license and SAFEA registration like those below (not a photocopy or low-resolution scan which are easily photo-shopped) they are undoubtedly a scam and you should not send them your resume or passport scan.
Get more details at
https://reddit.com/r/ChinaScamCentral
and also here at
https://reddit.com/r/TEFL_tips_traps_scams