[throwawaymaths]

Just take a deposit. Don't pay it back until they tell you they quit.

[MoSattler]

If my language teacher asked me for a deposit, I would find another teacher.

[throwawaymaths]

It doesn't have to be much. It can come with an explanation. If they are learning English, it's useful to know for the anglophone world ghosting (in many situations) is considered extremely rude.

I think Japanese people would be very receptive to this information and the $ incentive to let them know you're serious about it.

[jy1]

Structure as bulk "Buy 10 classes at a discount"

[dudeinjapan]

This is actually a great solution to the problem.

[throwaway426079]

From your username I figure you might know: are any other services sold this way in Japan?

I ask because if not then it's going to be difficult to go first. If yes, any idea how it influences behaviour?

[dudeinjapan]

Apartments come to mind. In my business we also help restaurants take deposits for reservations, which is now becoming the market standard.

[lozenge]

Homo economicus strikes again. Will the deposit make up for the emotional hurt?

[throwawaymaths]

It may overcompensate... Call me cruel but I'd have a very meta chuckle that it was economically worth X to the student to not have to message me!

[harperlee]

I was thinking more on the line of a subscription where you buy the hour of class, either if you dont show up.