It's a similar phenomenon to day cares dealing with late pickups. They have a few chronically late parents, so they institute a late pickup fee. Parents who always picked their kids up on time because of the implicit agreement now have an explicit agreement that it's okay to pick them up late if they pay a bit more. So the incidences of late pickups actually increased at the day care. You're exchanging a trust based system for financial interactions and some people have very different motivations.

https://www.jstor.org/stable/10.1086/468061?seq=1