You can set your car's availability using the calendar in your account, under "MY CARS", according to your schedule. Just click on the calendar to toggle whether your car is free that day, or set defaults by day of the week. Setting your car to unavailable means a renter can't even request it, and your car won't show up in searches for those dates.
When you receive a request from a potential renter, you can check the renter's profile and rating before you decide to accept or decline their booking. Remember, every member of our community is pre-screened and undergoes driver's licence and profile checks before being approved to rent.