right, but my worry would be that if you increase your revenue a lot when you switch from sending a bill and waiting for them to give you money to taking money

right, but my worry would be that if you increase your revenue a lot when you switch from sending a bill and waiting for them to give you money to taking money automatically until they ask you to stop, I would question how much of that increase was due to people forgetting to tell you to stop until after they've been billed. As I said elsewhere, I think the problem could be solved, for a pre-paid service, by giving an automatic refund if the user cancels within X days of getting billed.