There are other unrelated cases in which the introduction of money alters behavior because it turns an action/activity into a financial business transaction that's evaluated on that basis. One example I've heard cited a number of times is a daycare center that fined parents who were late to pick up their child. What happened was that some parents came to view the fine as just a late pickup convenience fee that they were happy to pay whenever it was easier for them. As a result, there were more late pickups because there was no longer a stigma attached to being late; you just paid the fee.