Is it even really cheating when taxi drivers charge tourists more? My mother clearly thought so, and nearly made us miss our plane by getting into a fight with a taxi driver on the way to the airport. But it doesn't bother me that much. In the case of Vietnam (not so much in Greece), the "cheating" will not make so much as a ripple in my budget, while making the cab driver much better off. It seems less like cheating than Pareto optimisation. I don't see any moral reason why I should be treated exactly the same as a native Vietnamese, since after all, I won't be, when we show up at JFK and wave our respective passports.