the practically optimal way to reduce stupid foreign tourists and criminal gangs is to put the high entry fees. I think more than
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THB per entry. Stupid foreigners and trouble makers are usually poor, that is why they are easily falling into criminals and illegalities. The truth is, real rich people never want to make problems at all. why? They have enough money to spend and enjoy. And they have also great future. Why do they make problems? That is like suicide for them. why they involve in illegal business? they have already enough money! no reason to risk on their life. Always, foreigners who are poor or short of money can get easily into criminals and problems. Because they have no bright future, nothing to lose. Also, Thailand does not want low budget or poor foreigners. They are mostly trouble makers. the practical way to reduce them is only higher entry fee or tourism tax. At least, 20,000 THB but much higher is recommended. As mentioned, rich people or good budget foreigners do not care much about that higher fees.