A year visa for Cambodia isn't $50, but multiple of it, and a letter from an employer or a business registration as well. And an additional work permit for $180 is necessary as well, without that you won't get a yearly extension.
I wouldn't be sure that the Thai immigration knows the difference between Kosovo, Croatia, Serbia, Montenegro and North Macedonia.. I guess they'd just throw a dart at the map and send you where it lands.
It gets refunded after cancellation. Expedia refunds it, so it just a few days (not a few weeks like airlines). Not all flights though, during booking you can see that 'free cancel in 24 hours' tag next to the valid offers. You can cancel online just with a few clicks after booking.