Years ago before the smoking ban I found a cigarette smouldering away on the edge of my cab after someone (a friend!) had just finished his spot on the jam night! It hadn't burnt the cab, but since then I get up and check the gear after every jammer.
Being expected to supply free gear hire is taking a liberty, and no one is going to replace anything that they break, or even contribute to the repair, so it just isn't worth it.