i don't know with you there, but teachers here are underpaid, so out of "creativity" and "resourcefulness" we have to go to different sources of income, that's for my wife, but nothing illegal of course, but this is too much.
The ads could also be very distracting. Exams are time-consuming enough. :/ But I do understand the desperation. Teachers are generally underpaid. Which is weird because it's one of the most important jobs ever.