Daft as it sounds, it is actually quite easy to damage the underside of a rented car. You're on unfamiliar roads (some with less than perfect surfacing) and its easy to suddenly come across a rock while parking or driving on a beach road.

A cracked sump or similar could easily set you back 1500 euros not to mention roadside assistance or a change of rented car.
(See Note 1 below)

Ok, this is a lot more unusual but it does still happen. Car rental companies regard damage to the roof of the car as outside the scope of bodywork. Damage to the roof can be caused by negligence - carrying things on it with or without a roof rack, or just coming back to the vehicle to find something (or somebody) has fallen onto the roof.

Paintwork damage to the roof could cost you around 500 euros, dents come a bit more expensive at around 800 to repair.
(See Note 1 below)

A lot more common, this can be caused by road conditions, a nail or sharp object on the road (beaches are particularly good for this one) or just a defect in the tyres themselves. Either way, the car hire company treats tyre damage as an exclusion so you will be paying for the rubber!

A single tyre (the rubber bit) comes in at around 300 euros a piece.
(See Note 1 below)

Isn't wheels the same as tyres? Nope - not when you're paying it isn't! - Damage to the wheel trim (embellishers) or alloy wheels is renter's responsibility too. Most common cause here - kerbing the car or the hub caps "mysteriously disappearing" during the night.

Wheel embellishers (they used to be called "hub caps") will cost you around 100 euros a pop. Damage to alloy wheel trims is considerably more expensive.
(See Note 1 below)

An old favourite on insurance claims. All it takes is a flying stone chip and WHACK - you suddenly have a massive bill to settle at the car rental desk. Glass cover also includes the side and rear windows, which are sometimes broken to gain access into the car to steal objects or shopping left on display.

A full windscreen can cost 2,000 Euros, side windows come in cheaper at around 500 Euros a piece.

Damage to the wing mirrors is a pretty standard exclusion on car rental contracts. All it takes is a truck to come a little too close while you're parked up and you end up picking-up the bill (as well as the pieces!).

Reckon on paying around 300 euros for your average motorised wing mirror!

Taking your car keys swimming can be a very expensive past-time. All car keys contain embedded chip devices which must "respond" to a signal from the car to start the engine. Getting the car keys wet (even by accident), or losing them altogether will probably require a vehicle change on the spot.

A new set of digitally encoded car keys for your rented vehicle is between 100 - 500 euros depending on the model.
(See Note 2 below)

Could be defined as "just being stupid", basically you will be responsible for all damage caused to the car if you :

- Drive under the influence of drugs or drink.
- Break the traffic laws.*
- Used the car for racing or competition purposes.
- Put the wrong type of fuel in the tank.

*Including (but not limited to) speeding, crossing solid white lines when over-taking or turning right, jumping traffic lights, driving on the wrong side of the road, over-loading vehicles with too many people etc.

Crashing a car because you broke the law as above could cost you the replacement value of the vehicle (6,000 - 18,000 euros) on the spot. In addition, the full value of any parking fines, speeding fines etc will automatically be billed to you (plus a handling fee) by the car rental company.

In really serious cases, you may also face prosecution locally and there is (obviously) no insurance policy that covers breaking the law!