Its my experience after 4 years living here, that a poker face is the best face, and nothing can be gained by risking having your laugh misinterpreted as a mocking laugh, which it actually is.
But there is an update on the OP.
On Saturday I bumped into an old BM , who had interests in the failed Go Go that was once above, on the 3rd floor and now lives in Cambodia.
He said that his ex now worked at Season+ and the waiting staff now had a good scam going on the owners.
This is because the second beer you order, if you are silly enough to hang around, is 'normal' prices' ( 150 baht IIRC) .
So the staff tell the cashier, who cant see the crowd, and cant keep up with the pace even if she could, that the 'first order customer' , billed at 900, is actually a 'second order customer' and gets a bin of 150 to present to the first order customer, but actually presents a bill from a secret pile in her apron that says 900 or 500 ( her proffered discount price). Then she pockets herself 750 baht or 350 baht , on one drink!!
He said they pick there marks, usually the lone or paired 'first order' customer, but still make a pile.
It kinda makes me feel good to learn that the Con Men are being conned...