Never have I known people so obsessed with making a quick buck, but at the expense of long-term gain.
I put it down to their dumbarse pride in having never been colonised.
It is all well and good to feel overwhelming nationalistic pride at being used as a virual English Channel by the English and French, who were used to being separated by inhospitable terrain (sea), and thus decided to decree Thailand as a similar barrier (but who could and would have invaded in days had the other European power not been so close by).
As a result of the above "achievement", I believe that Thais are brought up to believe that they are unusually cunning, and that the chance to use this to get one over on a westerner should never be missed. However, the sad fact is that doing this will likely lose them repeat business is massively over their head.