This happens all over the world - New Zealand, Singapore, Australia, Thailand, France -- even in Zurich airport! They are required to ask whether you would prefer to pay in your billing currency, and at most retailers when you sign the slip or enter your pin there is an acknowledgement that you have agreed to the conversion. Another reason to always check the details before you sign the slip or enter the pin (the currency and amount appears on the screen)

I have only once experienced one retailer (in Asia) who refused to accept the local currency because they 'didn't know how to change the settings on the machine', but as I prepared to leave the store they magically remembered how to alter it. One tip - if the staff member asks the issuing country of your card, don't tell them. There is no reason apart from this system to ask for that information.

This thread may be better located in Travelbuzz?