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A magazine Reader's Digest organized an interesting experiment.
Their reporters "lost" 12 wallets in 16 cities around the world. They left the wallets in different areas of each of the chosen cities, places like shopping malls, or in parks, or on the sidewalk. In each wallet there was the equivalent of 50 dollars in local currency, a family photo, and a couple of business cards with a name and phone number. A reporter waited somewhere near each wallet to see what happened. Another reporter answered the phone when people called to report the lost wallet, and then met the people and asked them why they returned the wallet.