On the bright side, the idiots who join these groups hoping to scam others tend to lose their shirts as well. The person orchestrating the pump-and-dump scheme bought the currency at $X per coin in question long before, and he's using the people in the group as patsies. "Buy the coins at $X + $Y, and the rise in price will make it so that you can sell the coins to some other idiot for $Y + $Z!"

If there aren't enough "outsider" idiots to buy the coins for $Y + $Z before the correction happens, the "insider" idiots lose their shirts. The original person, of course, makes a tidy profit.

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I learned this the hard way playing Runescape as a 16-year-old. 2007 was an interesting time for that game.