Purchased some tix for a local walking tour of Quebec for a trip in a couple months. The tour operator uses PayPal services to settle bills. If you decline to use your PayPal account, you can use a credit card, which I did. I already had seen the bill racked up in Canadian dollars (CAD). But one screen before the "submit to pay" page comes up, the amount suddenly changes to US dollars. There is a link in small print for "other conversion options," so I click that, and I can select to pay in the vendor's original currency. I did that and dodged a pretty sneaky DCC attempt. On the first page, the only amount showing is the already converted US$. (No I didn't check to see how bad the rate was.)

Beware!