Yeah. Really the only way to get through to them is to sell them books since you subtract that from the number to beat. So if they buy a few books, their number to beat is no longer 20 the next time they come in.
I’m not super into the capitalistic aspect of that but I didn’t want to introduce yet another number to track, like amount of times visited and subtract that. I guess I just wanted to keep it in theme and simple so I landed on books sold.