If a rock falls from the sky and cracks the windshield of your rental car, you are liable for the damage. This point is made clear, somewhere deep inside your rental car contract: you are financially responsible for any damage to the car while it is under your care, whether you caused that damage or not. You certainly already know this, but it still may not sway you to purchase additional insurance for your rental car. After all, what are the chances it will happen to you?

It can happen to you

It's true that the chances of your rental car incurring damage aren't high. But it's also true that once your rental car does incur damage, that probability becomes irrelevant. Here's a scenario to consider:

You arrive at the airport, pick up your bags and head to the rental car service counter. You fill out the paperwork, and are told to select a car from the parking lot. In the parking lot, all of the cars are parked outside. Airplanes are flying overhead. You find a car, throw in your luggage and you are on your way. Two days later, you drop the car off without incident.

Three or four weeks later, you receive a later from your rental car company. If the letter comes from Alamo (which is now part of Enterprise), it may say: "Our Damage Recovery Unit has received notification of damaged or loss to the vehicle you rented...If you have not already done so, please contact your insurance company and/or credit card company to report this claim to them."

Your word against theirs

At this point, there's no way for you to prove that the reported damage didn't happen while the car was in your care--even if you never saw the reported damage. Indeed, it isn't inconceivable that a rock did fall from the sky and put a tiny knick in the car's windshield, before you slipped the keys into the door. But alas, it doesn't matter. That damage is your responsibility.

If you dispute the claim, the car rental company will notify the management of the drop-off location that reported the damage. You can expect those managers to confirm that the damage is, without question, your responsibility. From there, you have no choice but to figure out how to pay for it.

Do your own walk-arounds

According to an Alamo representative, the counter attendants in airport service centers generally don't do "walk-arounds" of the vehicle before you drive away; they simply don't have the time. Therefore, the only way to protect yourself against paying for pre-existing damage to a rental car is to do your own walk-around. Inspect the car carefully and make note of all scratches, knicks and dents. Then go back to the service counter and get someone to document those damages. Don't expect this process to be easy either; if they don't have time to do the walk-around themselves, they may not be thrilled by your request.

When you return the car, ask your attendant to inspect the car immediately. Ask for something in writing indicating the car had no damage when you returned it. Be prepared to wait. If it's a problem, you can always take pictures of the car after you hand over the keys.

After the fact

Once you've already been stuck with the liability, you can use your car insurance, any insurance provided by your credit card issuer, and your own money to pay for the damage. First, verify your deductible on your insurance policy. Then, check with your credit card issuer; sometimes, the card-provided insurance will at least pay the deductible. If you don't want to risk a rising auto policy premium, you can collect on your card-provided insurance and cover the remainder on your own.

Catherine Brock operates BrockComm Travel, an online travel agency specializing in Long Beach cruises, Las Vegas party trips and other fun, unique vacation ideas.