I have frowned at this issue off and on for a long time, and finally looked into it more carefully. I didn’t like what I found: customers that pay for my e-books in anything but US dollars get a price that’s quite a lot higher than the exchange rate. For instance, right now, even though the Canadian price should be a bit better than the US price — about 2% cheaper — instead it will be shown as 10% more expensive! If that seems like a bad deal, you’re right (and congratulations on your math skills). My payment processor, eSellerate, is charging a steep fee for payment in your own non-US currency. Credit card companies don’t exactly give you the most favourable exchange rate when you buy in a foreign currency, but many do not gouge this deeply. My own card charges very little: it’s not exactly the exchange rate, but it’s nowhere near what eSellerate takes. eSellerate spins their policy as offering a “gauranteed” price in your currency, so there are no nasty surprises on your credit card bill. In other words: “Give me $10 and I’ll make sure no one mugs you in the next block — you’re safe with me!”
Bottom line: buy my e-books in US dollars and let your credit card do the exchange, unless you know that their fee is even worse than eSellerate’s.