As far as user is given a choice, it is buyer beware.

But most of the time, choice is NOT given. Merchant after merchant in UK and elsewhere in europe have told me that DCC is automatic and they dont know how to stop their machine from doing it. Circling local ampount and writing "DCC decline choice not offered" and then disputing the charge seem to be the only way.

Even when choice is given such as Ryanair, it is so hidden and difficult to decline that I consider it as scan in layman's terms.

(when it is small amount, I just swallow it as cost of being a tourist in foreign country or insist on paying by cash)