I'm sure there's potential for fraud but they're going to have the account info and billing info of people who rented the car time. If someone damages or dirties the car, they're going to be liable and probably kicked off the platform. All the car needs is a camera and a way for riders to complain about past transgressions that are leftover in the car and it'll probably sort itself out.

You could also pay people to manually remote into car cameras for a brief quality check after every ride. Wouldn't be that expensive. An interesting problem to solve though.