I can not stress enough how important it is to have a physical copy of your National reservation in hand while at the counter. Twice now I have made a reservation on the National site only to show up at the Europcar counter and be told that the rate would be 2,000 EUR instead of 600 EUR. The first time I didn't have a printout, so I paid for internet access in the airport (9 EUR) and was able to show them the reservation. They then gave me the National rate. The next time, same thing happened, but I had the printout and they changed it right away.