make a living

Neither as it stands, Alex. The preposition needs an object.

What do you mean object?

He makes a living on that.
He makes a living off that.

'That' is an object, but an inadequate one, because 'that' could mean a boat, a trade, or many other things, some of which might use 'on' and others of which might use 'off'.

Which do you use here?

He makes a living setting people up.

He makes a living off love. He makes a living on love.

A hokey player who makes that shot almost all the time.

He makes a living off that shot.
He makes a living on that shot.

sorry again

'Off' seems better.

He buys X for 10 dollars and sells it to his friends for 20 dollars.

Is this natural at least one of them please?

He makes money off his friends.
He makes money on his friends.

Thanks