Must I fill up the tank before returning the vehicle?
In Crete, we use a different method. Just return the vehicle with about the same amount of fuel that it had on delivery.
We of course always ensure that the tank will not be completely empty upon delivery.
The method is better than it looks as it e.g. avoids collecting and handling a security deposit for fuel, and we will also not charge you any enormous surcharges per litre to let our employees fill up the tank.