Earlier quoted context omitted.
Not to mention, do you really trust 20 strangers to treat your possessions as well as you do? Have these people never been in the back of a taxi, or any kind of public transit?
I've pretty much abandoned Zipcar for this reason. In the early days, it was great. But once membership increased, there was an increasing chance that I would get a car that was not particularly usable. Filthy on the outside (dirt, mud, etc) and/or inside (dog hair, bodily fluids, etc). Or a car that had one or more warning lights illuminated (check engine, brake, no wiper fluid, low gas, etc). And each time I had to…
Less hassle with verifying who actually trashed it, but also if you have to stare someone in the face after your ride, you'll probably be more respectful of the car.
But really, there's just not a satisfactory solution I can think of to make me want to use the service.