Not all employers are legit- there are plenty of horror stories out there. There are blacklists for some countries- Korean Black List
There's no official list and unofficial lists would just get filled with shills saying how wonderful places are.
Check schools out- do a whois search of their website, search on forums for people who have taught there, etc. If you are at all suspicious, don't accept the job. If they are evasive about basic questions or make unusual requests, then it's probably better to play safe.
There are plenty of good schools and ones that are OK, so it's far from all doom and gloom. The best protection you can have is to make sure you always have your fare out of there- that way you can walk out of a bad job. If you don't have this, then you are dependent and in a weak position.
- For Teachers