I have written this before on other threads.
If someone is taking private lessons or tutoring please look that the teacher is at least registered as self employed (small company) and paying social security like AHV a.s.o or the students or parents who takes the lesson make the necessary registration at AHV for this.
Information can be found here
http://www.keine-schwarzarbeit.ch/
The fine by an authority control without this is not very low …