One of the “impromptu” tricks that I do is the mismade bill. It’s an amazing trick, and I’ve got a great routine for it. The flow of the trick is that I borrow a dollar, rip it up and it ends up mismade. I leave the dollar bill with them and don’t restore it.
When I do the trick I normally don’t turn it back, I offer to buy the dollar bill back. It’s a much stronger trick to leave it messed up and give them the option to keep the bill. If they want a dollar back, I simply give them a fresh dollar out of my wallet.
Here’s why I never turn it back. People at that point try to bust you. They’ll remember the condition of the bill, or serial number and call you out on the switch. You are in a much better position buying back the bill with a separate dollar or ideally letting them keep it.