The distance traveled and fuel level are automatically calculated by the telematic box installed in the car.
If you have made extra kilometers beyond those included in the reservation or if you return the car with a lower fuel level than the initial one, you will have to pay the estimated extra charges after the trip.
For fuel, the price per liter of fuel is set at the national average price defined by the Ministry: https://dgsaie.mise.gov.it/prezzi-mensili-carburanti