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> But, say, once I was in Bangkok, that same flight that was once $300 would fall to $30 almost inexplicably. This phenomenon is because a ticket’s point-of-sale—the place where a retail transaction is completed—can affect the price of any flight with an international component.
The reasons are pretty easy to understand. When you try to book an in-country flight in Thailand from the United States or Europe, they infer that you are someone who will soon be traveling on an expensive international flight to Thailand. They infer that you will accept $300 for an in-country flight rather than say "screw this, I'll take the train or bus", because (1) you can afford international travel so $300 probably isn't a big deal to you, and (2) there's a good chance you are on a business trip and need that domestic flight to keep things on schedule.
When you try to book an in-country flight from within Thailand, those inferences do not work.
At some point, they'll get clever and look at your IP address when you make an online booking, and even if you are booking in-country they will give you the $300 rate if you are connected through a hotel that is popular with international travelers.