Their website uses your IP address to work out what currency it charges you in. So if you just happen to be in Russia and want to book a car for when you get back to Heathrow, the website charges you in Roubles. So even though you pay using your UK debit/credit card, you get slugged with exchange fees as it takes money out of your UK bank, changes the currency into foreign currency, then back into GBP. I thought I'd seen it all, but no, rentalcars.com takes the prize for the most stupid booking system ever conceived.