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.
They might be able to clarify if it's their own rule, or Thailand's policy, though. The single-most-powerful person in your travel process is the gate agent that checks you in before your first international leg. If they're not convinced, you're in trouble. So I'd try to get anything in writing that you might need regarding Thailand Pass and rules per Unvaccinated travelers. Also best if you can get an email response from the airline
If it's an airline rule and they don't let you board, your Thailand Pass may be irrelevant. I'd make 100% sure. The airline may put that rule in place to avoid controversy with a potential unvaccinated traveler testing positive and forcing nearby vaccinated travelers to quarantine (yes, I understand the complexity and irony, but trying to see their "logic")