IT building is great as you can get it done without prep or knowledge. It does require you to go 4 steps and waiting at every step and only get to actual immigration at the last step. But every step is to make sure you have the right documents and if not they can help you. So here best to come early to avoid long waiting, which could be all afternoon if you come after lunch.
If you know exactly which documents you need, the photo and copy of your passport I would upload it with the via government office e-extension and make a pick up appointment a few days later. The website doesn't explain the requirements very clearly.
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In both cases there are shops where you can get something printed and your photo taken if needed.
I'm sure there are unwritten guidelines lines that they use and may change all the time. I can imagine that at BKK with the large amounts of incoming people they are less critical than DM.
And on top of that yes how the officer thinks of you may have an affect
Yeah, been going in and out for 7 months, with 2 extensions.
My experience so far, is never a problem at Suvarnabhumi airport.
At Don Mueang airport, it got increasingly more strict with more stamps and this many entries.
1st time no questions or proof of anything, 3rd entry, just more stern questions and stamped. 4th entry here, got seated in the separate area to purchase and show forwarding ticket.
So Don Mueang seems more strict and also get the feeling female immigration officers tend to be more strict, not sure if that's true or not.
I've crossed that border, not for a border run though. And I wouldn't call it a "good" crossing, it's very old fashioned, slow and laid back. Not very clear what is where with signage, at least in English.
So a bit of an adventure.
Note that you can only do a land border visa run 2 times a year in Thailand.
Officials just sit inside behind the glass service desk while some Cambodian hustlers will help you for a small tip, nothing to worry about, I paid 20 TBH when he asked for a tip at the Cambodian border.
The forward travel question at the airport depends on your passport and any other thing they may have doubts about. So I'm guessing here as well.
Having a European passport myself, I've never been asked that in Thailand and neither at this land border.
Also this is a known land border for visa runs.
When I crossed over to Cambodia there were 2 guys from US that went straight back in to Thailand, which they've done before.