Aside from the illegality, I mean.
From the Korea times:
A Korean private tutor was caught earning more than 150 million won ($130,000) a month, without paying tax, from illegally teaching students in an apartment in the affluent southern Seoul.
He allegedly taught a group of students in a 337 square-meter (102 pyeong) apartment, charging about 10 million won per student per year. This is the first time that a tutor who has taken such a large amount of tutoring fees has been caught.
Let’s see. A hundred and fifty million won a month. That’s one point eight billion per year. One hundred and eighty students per month. How do I compare?
I have 7 classes at about 20 students. 140 students.