Defer vs immediate -- kind of sneaky. "What happens if I don't lock it in now? Better press immediate". I know many infrequent travelers who would fall for it. I would hope that visa and Amex would educate us. " pay with your visa and select USD to get the best rate, another advantage of using your card vs cash!"

as an aside, it pays to educate people. I was recently texted by a friend on vacation in Morocco who remembered my boring discourse on DCC but didn't register the logic. He sent a picture of the terminal, asking me what to do. He's a uber smart guy and generally sophisticated -- MD, MBA, military Academy -- sat thru my boring dinner dissertation and still got confused. He said one place hovered around 10% which kind of shocked me.