I have been to some of those type of tourist places myself. One I went to I saw the guy behind the rail (helping people). When somebody would ask him if they found anything good he would look at it and say nope not this time and then throw it to the right or left depending on which type of stone it was. I saw him throw a emerald which was black to one side of his area and then throw another to the other side which wasnt good at all. I bet he had some good ones when everyone else went home and he didnt have to pay a penny for them. Just so you know next time you go or if anyone tries this type of thing. Keep all of your colored stones you find. I got some good stones that day.