You cant get a DTV on arrival. You have to apply through a Thai embassy prior to departure. Their policy (last I saw) suggests applying no more than 45 days and no less than two weeks from the date you wish to fly.
There are several Thai law attorneys on youtube that have discussed this. Here’s the gist:
The law is pretty well managed on this. Provided you are not maintaining a Thai bank account, your funds don’t functionally exist in Thailand. As such, they are not taxable. It isn’t until you import funds into the country that they become taxable.
So, either operate without a Thai bank account or prepare to pay taxes on the sum of all monies imported to your Thai account(s).
There is no reasonable way for the government to track ATM withdrawals, so those are functionally safe.
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