Have you ever returned your rental car and then a week or two later found a mysterious charge on your credit card from the car rental company? This is one of the most common complaints, the charges that appear after the customer returned the car and everything seemed fine.
Post rental charges can be for a number of things including:
Damage caused to the car during the rental period. Toll road usage charges. Extraordinary cleaning. Late return. Missing fuel.
Missing fuel is by far the most common charge (closely followed by damage charges) and one that is appearing more and more often. Most companies offer options when you pick up the car to pre pay for a full tank of fuel allowing you to return it empty without having to worry about filling up just before you drop off the car. In countries like Spain and Portugal some companies actually enforce this as their standard policy, often charging the full tank at a much higher price than you would pay at a petrol station, a way for them to offer low up front prices but then make up the difference when you pick up the car.