You are not required to clean your vehicle before returning it – all rental cars will be serviced by the car rental company for the next client. Most of the car companies do have extra charges that can be as high as $75 to clean a car with excessive or unreasonable amounts of dirt etc. So if you have been going to the beach and notice a lot of sand in the vehicle, or there has been something sticky spilled, it is always a good idea to vacuum it out while you are filling the gas tank before returning the vehicle so avoid getting charged for excess cleaning.