Hi Maisy, yes it is a hidden cost. It is just like going to one travel agent and changing your money at a rate of say 1.9 dollars to the pound and going to another who is changing it at 1.8. The midway exchange rate in this case (the rate they buy their dollars) would be about 2.1 dollar to the pound, so they make the difference. The same with most credit cards, they add around 2% to the exchange rate