Is it comission-free to cash American Express travellers cheques at Heathrow airport?
most of them will charge you commission, even the american express booth in the terminals, if you don;t have local currency in hand, which u can get from your local bank back home. then change a small amount at the airport, and find an american express shop in the city your visiting, or check the local banks, competition for trading money is big so a lot of banks wont charge you to exchange or may charge a few but give u better rates than the airport the airport takes advantage of some travelers trying to cash in the last amounts of currency, so do some shopping with local banks and of course the local american express shop.
