I dropped off a Hertz car after hours at Luton airport in England a few weeks ago and noticed a 130 pound debit on my credit card a few days later. When I queried it, I was told it was a refueling charge as the car was returned empty. It was only a small car which would cost nowhere near this on an empty tank. Luckily, i'd taken a photo of the fuel showing full and had a receipt from the gas station, but its certainly annoying when this kind of thing happens.