Question: We recently traveled to Spain and Portugal. When paying by credit card, we were given the option of paying in euros or dollars. It was unclear which was more advisable. I carry a co-branded airline credit card that doesn’t charge a foreign transaction fee, so if you can pay in dollars and not incur a foreign transaction fee, then there is no reason for us to be paying a $95 annual fee for a card that doesn’t charge the fee. Are we missing something? — John Martin, Glendale, Calif.

Answer: If you’re paying in dollars, you’re probably missing a chance to save money.

Here are the five words you never want to say when you’re abroad and you’re asked which currency you want to pay in: “I’ll pay in dollars, thanks.”

That’s because of a devilish little deception called “dynamic currency conversion,” which is not the same as a foreign transaction fee. It’s another fee altogether.

Here’s what happens, according to Kimberly Palmer, a credit card expert at NerdWallet, a personal finance website:

When you are asked whether you want to pay in dollars or euros or any other currency, you are allowing a dynamic currency conversion provider to set the exchange rate.

You pay its rate and, Palmer said, “In most cases you will end up paying more … if you say yes. It’s because the exchange rates are not generally as favorable as the card network’s (meaning Visa, MasterCard or whatever credit card you carry).”

The provider and the merchant generally split the profit from that conversion fee. It won’t be much on any one charge, but for lots of transactions it could be a pretty penny (or euro).

What they’re doing is not illegal. It is said to be a convenience: You know what 47.52 means in U.S. dollars. You may not know what 37 euros is immediately, so why not?

Here’s why not: You’ll generally pay 1 percent to 3 percent more for paying in U.S. dollars than you will if you pay in the currency of the country you’re in, Palmer said.

But you don’t have to get stuck with paying a premium abroad. You can avoid that pain by:

>> Carrying a credit card (or cards — Palmer suggested having two or three in your wallet) that does not charge foreign transaction fees.

>> Choosing to pay in the currency of the country you’re in.

>> Watching the merchant like a hawk.

I did not swell with pride when one hotel assumed I’d want dollars and ran my charge through accordingly. Not wanting to cause a scene, I didn’t speak up.

Any merchant accepting a card is supposed to ask which you want. This hotelier did not. I’d assume evil intent except she looked about 12 years old, which is not to say that scam artists can’t be young, but I’m giving her the benefit of the doubt.

Should I have said something?

I could have, Palmer said, but it’s just as easy to keep your receipts and contact your card company when you return home.