Guess I got lucky, that the staff at Al Molo knew how to do this, and I insisted seeing the confirmation slip.

To me, it's very probably that Greyhound Cafe/Coyote guys didn't learn how to operate the opt-outs. Of course the acquirer is the main culprits here, but since some of the Global Payment merchants know the stuff, I still blame the ones that don't do their homework.

My guess now is that all terminals in HK, if they cannot disable DCC preemptively, they should have the feature to opt-out later by calling the transaction back. I remember at Al Molo they keyed in the trans/batch/or whatever 6-digit number of the transaction, and pressed some selection keys, then I got the confirmation slip showing only HKD.

BTW, their markup was 4.2%, stated on the currency selection slip.