Up until a week ago I had two cars. A Corvette for when the sun shines and a 10 year old Mitsubishi 380SX which I used for carrying more passengers (the Vette being a 2-seater) and for when it is bad weather, which is a lot of the time in New Zealand right now because it is winter. But I was paying registration, insurance, maintenance and when the Mitsubishi wasn't being used it was still getting really dirty from tree pollens etc.
There is a local business in my suburb which allows people to rent out their own vehicle when they don't need it and given that the car was in great condition (it used to be my company car and when I left they let me buy it at book value, way below resale value) I was reluctant to sell it.
What put me off sharing it was the risk that people would thrash it or leave it in a mess. An ex boss used to own shares in a yacht, like a time share, but every time someone rented it, a broker would thoroughly clean it, just like a hotel room and it would be spotless when he used his time and when he brought it back, he could just walk away without having to do all the work that boat owners normally do when they have been out for a weekend.
In the end a nephew was leaving home and needed a car and I decided to let him have it below market value, knowing that it was big and safe and he would easily get another 100,000 km out of it without any major costs.
Car-sharing is coming and perhaps it will be well managed, like AirBnB where people are rated and respect other people's property, but when a car might be rented for an hour, perhaps multiple times a day, for as little as $8 an hour according to GM http://www.pymnts.com/unattended-retail/2017/general-motors-maven-drives-unattended-retail-and-urban-mobility/ there isn't the implied value that people would have when renting out a boat.
So would you rent out your car?