Save your receipts, and check your car over carefully before you take it…read more
Although the terms are not really found anywhere on the web site to describe what happens when you don't bring the car back totally full, what happens is that you get overcharged--sometimes even if you did bring it back full. This happened to us on our last rental here. Refilled the car, brought it back full, got charged for 4 liters of fuel + taxes + a refilling charge anyway, to the tune of about 25 euros. When we asked them about it they said "maybe it is a mistake" and that they would refund it if we could show proof of refilling. Only by chance we still had the receipt from the gas station, but we still had to make an extra trip to their not very nice rental location next to the not very nice train station. And at that, they were not able to refund the fees immediately, because we came on a Sunday, so we are still not sure whether or not we will actually see the refund. Although we reserved the car online, so they obviously have an email address, we never got an email about this charge. It all seems quite shady.
A quick google search suggests that other folks have had similar issues, sometimes getting charged for pre-existing damage. Proceed with caution!