(Paid) Flight Instructor
If you expect to be paid, expect to encounter all of the headaches that go with being a "paid professional". Liability insurance, some sort of standardization, licensing? Expect to be sued if you charge someone $25 an hour, spend 8, 10, 12, 16+ hours teaching someone to fly (keep in mind at a minimum now the student is pushing $1000 on his "new hobby") and after his first successful landing he crashes while trying it on his own. Think it's perposterous? Let's not forget that lawyers are (or were) suing MickeyD's for "making" kids fat.
Spend 20 hours getting paid for instruction teaching someone who just can't get the hang of it, decides to quit and wants his money back because you couldn't "teach" him....
Now, if you are talking about some sort of advanced class or school, teaching some of the finer points to those who are already insterested, invested and willing to learn, that's a different ball of wax. In this case you have a greater expectation that your audience will be receptive and has a desire to learn. I believe there is a difference between the newbie who has just dropped $400 for his new Alpha trainer and AMA after watching a couple of episodes of Inside R/C and the seasoned veteran and his 33% IMAC plane who wants to learn more about setup and aerobatics.