In fact, there are two companies that are like "AirBnB for cars". I don't know if they're in the Seattle area though: Turo & GetAaround. They offer insurance coverage for when the cars are rented out, like AirBnB and of course they offer better insurance to the renter during the reservation, for a price. Car prices are set by the car owners, based on car type, age, etc. You meet up with the person whose car you're renting, although some GetAround cars have some technology installed so they work more like Zipcars or Car2Go cars, so that you can get into it if you have a reservation w/o needing to meet up with the car owner.