Well, that's part of the problem. People give them money to "go away". Then they are trained to hassle you because you will pay them to go away. I'd just tell them no and keep moving. In the past I have put my cell phone to my year (not really making a call) ...
"This is detective Morrison. I got a black male who's becoming violent. I need some backup at my location immediately"
They usually take off like a shot. The first guy I did that to was hopping around on crutches asking for $ and was being a pest. When I did the above scenario he threw the crutches down and sprinted away across parking lot. He even had some cloths wrapped all around his shin to look like an injury.
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In the beginning, the patriot is a scarce man -- brave, hated, and scorned. But when his cause succeeds, the timid join him. For then, it costs nothing to be a patriot. -- Mark Twain