When you rent a car, you'll walk around it with the rental
company agent and look for any damage to the vehicle.
This information is marked on carbon-copy form similar
to the two examples shown at right. There's not much
room to mark things on the tiny car illustrations, and
most tourists feel uncomfortable pointing out every tiny
scratch. But this process should be taken very serious.
Any damage not marked when you depart could be
charged to you when you return the car.
Some companies (or perhaps just the employees) have learned that this is a great profit center. We have had companies try to charge us for existing dents, scratches, and even a windshield (due to a tiny, almost invisible surface chip that I'm sure they had charged numerous tourists for!). We've heard that other popular items are hucaps, jacks, spare tires, floor mats, trim pieces and bumper pads. Don't think that using a major international company will protect you from this. Our windshield episode was with one of the biggest names in the car rental business. Luckily we didn't have to pay for any of these because we had purchased the full-coverage insurance.
Check the exterior and interior of the car carefully and mark all scratches, dents, tears, cracks, chips, or loose parts on the inspection form. Also, make sure there is nothing missing from the car like the antenna, door handles, knobs, buttons, hubcaps, spare tire, windshield wipers, jack, fire extinguisher (must be in the car by law), gas cap, and most importantly, license plates.
If you park illegally in Mexico, the police will take your license plate. When you return your car without a plate, the rental car company will have to track down which police station has the plate, pay the fine, and send someone to pick it up. They'll charge you a hefty fee for the extra work. Make absolutely sure that your rental car has a front and back license plate before signing the form. There's really no reason they couldn't remove a plate and just claim it must have been removed.