I've had this happen twice last year in Ireland, where they no doubt see a lot of American tourists. The first time it happened at a hostel in Galway, and I had them reserve the transaction and rebill me in euros. The second time it happened at a hostel in Dublin, and they said their credit card verification system automatically billed in dollars when they swiped my card, and they had no way to override it. As I was only paying around $30 a night for a dorm bed the difference might have worked out to $1 a night for each of 3 nights, but the only real option left would have been to leave (or have enough euros on hand to pay them).