Rick Steves has a great piece about avoiding pickpockets and scamsters on the streets of Europe, although his advice is valid anywhere you might travel.
He recommends wearing a money belt, staying alert and learning to recognize scams. Put me in mind of a friend whose wallet was lifted by a little old lady on a bus in Ireland, of my mother being boxed in by two men trying to get at her pocketbook on the subway in St. Petersburg (Russia, not Florida), a cab driver trying to charge me 10 times the going rate in San Jose, Costa Rica, and a dozen other stories.
It happens everywhere, folks. Tourists get taken in the United States, too. I once saw a police office at Rockefeller Center in New York City screaming at a hot-dog vendor who had ripped off a Japanese couple. They got their money back.