The only thing that worries me is that Will Bancroft who hires his Mondeo out through WhipCar mentions that someone scratched his car. They agreed on a figure, he buffed it out, all very civilised. I'm not sure that would always be the situation. Are you old enough to remember the friendships ruined by a scratch on a borrowed vinyl record. "It was there already!' was the usual reply. It could be fists at dawn over a car.
http://www.guardian.co.uk/money/2012/may/04/hire-a-car-use-neighbours