I don't see that as a similar issue. English-speaking Thai often get paid more, and to have to service someone who can't speak Thai may necessitate having a bilingual (higher paid staff).
In America, you pay for higher-skilled stylists (though I give you it wouldn't be acceptable to charge a Spanish-speaker more for service in their language).
Again, I'd be curious if they charge Thai-speaking farang the higher price.
I can use my chase credit card here and get good exchange rates (I pay in baht) w/ no foreign transaction fees. If you have a card geared towards travel, it's not usually a problem.
It would have to be offered as a service by the banks w/o requiring the vendors to engage with the card processor. The foreign card holder wouldn't be disadvantaged if the have a good travel card, and the vendor would likely pay a fee to their bank for the processor kickback. The biggest issue would be the logistics of how the foreign card holder would actually execute the payment--likely needing to set up a basic account.
Plenty of card providers offer "no foreign transaction fees" as one of the benefits, along with good exchange rates. It's not impossible if you can get Visa/Mastercard on-board. In that case, though, the vendor would be paying for processing (likely via a fee on their bank) unless it was subsidized.
Yeah, as I was writing it I actually thought: I've never personally seen a dual sensor, but you could get an idea of filter life/effectiveness, and even better if that sensor measures air flow, as well.
I think you'd likely just put the sensor pre-filter so it's analyzing the air going in--which should theoretically be a good indication. I'd agree that a sensor post-filter would only be useful as an indicator of filter effectiveness.