I certainly understand your example of not pursuing this on a business dinner charge (no problems, I am expensing it anyway); the rest of the time, I've not had trouble asking the merchant to void the initial attempt to charge me in USD and re-process the charge in local currency. Takes perhaps a minute more of my time, that's all. Two recent examples were in BKK at King Power duty free and at a hotel in CNX.

While I try to scrutinize every charge slip for this practise, it is easy to forget sometimes.