You should look into Turo. It's like Airbnb, except with cars. People that have an extra vehicle will register it with Turo and people can rent it. I've rented cars 2 times in my life, once from Turo and once from a commercial car rental agency and Turo was much smoother.
You can actually pick the exact car you want to rent, look at pics, reviews, etc.
People have their own fleets of cars on Turo now. Just like someone might own lots of Airbnb rentals.