When we checked out, we were charged city tax and paid 18 euros, the amount the hotel told us to pay. However, I later realized that the city tax per room per day is 1.5 euros, and since we stayed 6 nights, the city tax should have been 9 euros. Hotels are in the service industry and should not make the mistake of overcharging. Furthermore, since the mistake was made at check-out, it would be impossible to get a refund.