Originally Posted by
JohnnyRockets
How would they know who to charge $20. And on what grounds, since you are not flying out but just transiting.
Anyway, I think if you get your onward BP from the transit desk, don't head up but go straight to immigrations. I believe if they don't issue you a new BP landside they wouldn't know you are due tax if it even is a thing.
If you stay airside during a change of planes you have not technically entered the country. Once you go thru arrivals immigrations and get your passport stamped you are officially entering/visiting Thailand and not merely transiting.
And the 700 baht fee is a departure tax. Once you are land side and and go thru immigrations to board an international flight you are officially departing Thailand. As others have said they might notice it and they might not. YMMV but be prepared to pay it if necessary.
SL