Varies by schools, some of the pilot-mill type like Trans Pac and others can pay decent if you stick around, you can be making 40K in a couple years, but the QOL can be pretty bad and they try to abuse you. You end up working 6 days a week and long hours. Some of the bigger universities like UND, ERAU and a few others have a better QOL and not quite as much abuse, while retaining the same or higher pay. When it's just a small 141 school or part 61 school, all bets are off. A lot of it comes down to what you see as billable time and making it worthwhile for the student, rather than only "charging for engine time". Some things are inherently unethical, like charging for ground time during lunch at a destination or while the student is preflighting while you aren't there with them, but on the other hand it's easy to shortchange yourself. If you're supervising preflight because you are physically there, you should be teaching something, checking the plane yourself, doing something, etc, and that is billable time. The biggest issues usually turn out to be places that want to to show up and work for free for much of the day, essentially treating you like a "contract employee", rather than getting paid for all the time you are on property and doing work.