You are approached by a crook who is trying to sell you a beautiful arranged coin collection for, say, $100. On the box holding the coins, you see a name and a phone number, as from a previous owner. You ask the crook whose name is that and he fumbles a bit and then says, unconvincingly: “Oh, he gave them to me”.
The seller gives you a few minutes to check the coins and you get the phone number on the box.
So, not wanting to buy stolen goods, you ask the seller to wait a few minutes and you go, ring this number and ask him about the coins. The guy on the other end of the phone is really appreciative; he tells you the coins were stolen from him and he will pay you a reward of $200 if you can return them.
That’s where the scam happens. The owner and the crook are partners, and you will pay the crook a good chunk of money knowing that you’ll get it back – and then some – from the owner. Except that the address is fictitious, the phone number turns out to be a public phone in a bar and the coins are just useless fake junk, as you find when you take them to a real dealer.
How to avoid: never buy anything from people who approach you on the street.