There are required to ask you in which currency you want to pay. The only time I was not asked I called and had them cancel the transaction and charge my card in the local currency. I have a no conversion fee card, and these DCC rates are very high (usually +4 or 5%). Even with cards that do carry fees for conversion it is still cheaper to pay in the local currency. Retailers push DDC as 'very convenient' for the customer but there is nothing inconvenient with paying in the local currency - the bank will do all the work.