Now.. my advice might be this. IF asked to do a "Demo" under the promise they are
very interested in hiring? Then agree to doing a paid class. 200rmb maybe. IF THEY HIRE
YOU then say you will wave the fee.

Probably the best advice so far! Offering to waive the fee if they hire you will at least tell you if they are genuinely interested or not.

In fact it wouldn't hurt if this idea became standard-practice throughout the ESL industry in China. (IMHO)