There is a blacklist among English schools, has been for a long time. However, it doesn't seem to have ever had much use, and seems confined to a pretty small group, so I wouldn't worry about it.

Turnoi is on the nosey. If you "pull a runner" and can't get a release letter, you will be back at square one regarding your residence permit...you'll have to start that process over again. And teaching in China without a residence permit is a really silly thing to do.

The fine he mentions IMHO mainly exists to give schools a justification for keeping whatever salary or benefits you may have accrued. I don't think many people have ever had to pay more, but it is certainly possible. This is one reason I generally advise people that if they run (and running should only be done as a last resort, but I recognize there are times when running is the only choice left...) then it's best to go to a different province, putting you out of the reach of most people. Shanghai is big, but not necessarily big enough for you to hide in.