I do not think it is that clear-cut, even for car rentals. If the car owner knows or should have known that the one renting it was a clear danger, I think he should have some responsibility. I also think law agrees with that. If it does not, why then does one have to show a driver's license to rent a car?

The gray area:

- if the owner could have known of the danger, how much effort do we think he should make to find out what the danger is?

- how high a risk increase can the owner let go? For example, if a 18 year old with a whiskey bottle in hand and a couple of obviously drunk friends wants to rent 'the fastest sports car you have', is it sufficient to check that the guy has a driver's license and does not look drunk or high? Would a check that he is not drunk be sufficient?