When you’re paying for goods in another currency, whether you’re actually in another country or just paying in a different currency online, if you use your credit card then the credit card company and possibly your bank as well are going to charge you for exchanging the money over to your own currency.
The key here is understanding where each of the credit card charges on foreign currency transactions actually happen with the particular card and bank that you use.
In some cases the credit company will charge a percentage of the transaction for the change in currency and in others the bank itself will charge this percentage. In a few circumstances both the card company and the bank will charge you and it may not be immediately obvious where you have been charged, at what rate and what was actually just a fluctuation in the foreign currency exchange rate.
The best thing you can do…
Is ask your bank directly exactly what their credit card charges on foreign currency transactions are. There’s a good chance the bank will respond with an “it depends” statement but if you perserver then you’ll end up with a good understanding of the charges and will know when not to use your credit card due to the charges it will incur.
Remember that your bank is providing you with a service that you could get elsewhere so they should be there to help answer your questions and shouldn’t be trying to take more charges than necessary.