I don't care if a teacher is relatively more expensive, it's a free market after all. 

But what about teachers who all of a sudden raise 20% or more their prices? When you choose a teacher, either for 100ITC or 500ITC a lesson, there is an understanding -I guess -that you took the price into consideration as well. So, after a few lessons, when you are used to the specific teacher, is it really ok for them to raise their prices like that?

I guess you'll say to book packages, but the same applies there. Packages are 10 sessions at most, and you can't learn a language in 10 sessions. So, once you finish a package, the next one will cost significantly more. 

I believe existing students should have a price control option, or else a teacher could raise their cost by 500% just before your exam.

I repeat I don't really mind high prices, I just don't like the sudden raises.