The technical term for this is DCC, Dynamic Currency Conversion. It can happen throughout Europe, and it's not new. In essence if you use an ATM and you see, nearly immediately after selecting 50€ or whatever, a precise dollar conversion amount (in your case) or an amount converted into your home currency, that's a DCC rate. In theory competition should mean that an ATM bank will offer attractive rates to get more business, but it doesn't seem to work like that. 13% is a bit high, I would expect 8% to 10%. But yes, one should always decline since if DCC is not selected to goes to an inter-bank rate, which will be a far fairer exchange rate. As you mentioned, there may be transaction charges on top. DCC also applies in transactions, particularly when checking out of hotels, where the receptionist will ask if you want to pay in Euros or Dollars or whatever. Almost always the answer is Euros if that is the local currency. Incidentally, if you had chosen the DCC rate, it may be your host bank won't regard it as a native currency transaction and still charge a percent or two as forex handling fee.