There are phony begging rings all over the place around here. They have shift changes and everything. Because of that I almost never give money to beggars anymore. I give items instead - hats or mittens in the winter, food, clothes, water bottles, whatever I have with me in the car that might conceivably be useful and I can do without. I've seen people bite into a sandwich like they've never seen food before, and I've seen people who look at a sandwich like "WTF am I supposed to do with THIS?" Sadly, the latter is far, far more common than the former.
ETA: IME around here, most of the really down and out homeless don't really beg that much, anyway. They scavenge, but they don't actively beg.