Regarding the local guys and their game they play with tourist girls...
I saw the same thing happen in Cayman, but the guys there see it differently.
They see they are providing a service. They become your personal tour guide and date for your vacation. They show you a good time, where to go, what to do. They add alot to someone's vacation. But they cannot afford to be doing this every week. So instead, they let the girl pay for alot of what they do. While it doesn't sound like something you would expect on a regular date, they feel that it is sort of payment for services rendered.
In Cayman though, i have never heard of anyone asking a girl for money outright though. Sure, pay for drinks and dinner etc, but to ask for money, i have never heard of that.
Scamming any tourist is a really stupid thing to do. Toursist come to our countries to have a good time and spend their hard earned money. They don't need a few selfish individuals ruining someone entire vacation experience. All that person will remember of their trip is how they got screwed over. Local guys can show people a good time, and accept gratuity from them in a variety of ways, but be honest, that is all anyone really wants.
Just my opinion!