If you damage the car while it is in your possession, ensure that you notify the car rental provider as soon as possible. Unfortunately, regardless if the damage was your fault or not, you will be charged. You can purchase rental vehicle excess insurance to avoid this from happening. If you purchase insurance, you will be covered for the cost of damage to the vehicle up the excess amount. You will first need to pay the cost, however, you will be reimbursed.
When you first pick up your rental car ensure that you check the car for any damage. You will be given a vehicle condition report where you can list any damage on the vehicle. By doing this, you are notifying the car rental company of any issues before you have driven the car which means you will not be charged for that damage. You can also take photos of any damage so you have proof.
Once the vehicle has been returned, the car rental company will assess the car for any damage. If there is anything wrong with the vehicle, the estimated cost will be charged to your credit card. If the cost changes, you may be reimbursed for any excess. If you are unable to be there for the inspection, the car rental company will let you know about any damage with images. You will then be charged on your credit card for the cost to fix the car. Keep in mind that if you had taken the car to any areas that are prohibited, any insurance policies will be void and you will be liable for any cost to fix the car.
Read more about the process of picking up a rental car.