I think it depends on the shop, if they know you and how quickly you bring it back. If you are a regular, they will be more liberal if they think that it might jeopardize your continued business or if they know you well enough to trust you.
Also, if you get out the car and come back in 5 minutes later, they may consider that you didn't have time to copy it and take it back.
But most of the time, you buy it, it's yours.