You and I are one of few who consider 4% in mark up as a scam: most people wouldn' even notice.

Always make sure how much they charge in what currency before entering pin. Some countries such as Mexico, the amount doesn't show up on pin pad, so I've fallen in this 'scam'. They charged me in usd while I wanted to be charged in mxn, the spread was around 4% as well. After I left the store, I've noticed this, went back, I was told Americans are charged in usd. I told them that I'm not American! (I know, I know some ignorants at home think everybody who speaks Spanish is Mexican, they even think they speak Mexican, really? Can you tell their Mexican accents and vocabularies?) I told them that I wanted to return, then buy back in mxn cash. They said no senor, you already left the store, it's no return.

at pvg, they list prices in several currencies. As far as I can see, I'm the only one using a calculator! I decided to pay in usd (figured it'd be almost a dollar cheaper per carton), they told me they charge my cc in cny. I then asked if I paid in usd cash, if I get change in usd, they said yes and all was good.

in ist, as well as a few countries like Vietnam, the Philippines, and often Mexico, even international brand are cheaper in city than duty free. In ist, I bought lark in city. Duty free in Turkey often give heavy discounts to 2 and more cartons, but I'm talking about 1 carton prices.