The Rip Deal Scam
The Rip Deal: How It Works
The Rip Deal scam is notorious mostly in Europe but it could happen anywhere, as criminals target jewelers.
According to Wikipedia, "they would offer to buy some substantial amount of his wares at a large markup provided he perform some type of under-the-table cash deal, originally exchanging Swiss francs for euros. This exchange goes through flawlessly, at considerable profit for the mark."
"Some time later the scammers approach the mark with a similar proposition, but for a larger amount of money (and thus a larger return for the mark). His confidence and greed inspired by the previous deal, the merchant agrees—only to have his money and goods taken, by sleight-of-hand or violence, at the point of exchange."
The Rip Deal scam is depicted in the Matchstick Men (2003) movie, starring Nicolas Cage. Watch the movie's trailer below (full movie available, too):
How to avoid:
Needless to say, the under-the-table deals are illegal to start with and should raise a red flag right away. Do never get involve with criminals. They do their crimes daily, as a full time job, so obviously are better than you when it comes to getting the better part of the deal.