Oh, it's gotten even more complex than that, but the bottom line is you're left holding the bag for a check/money order/cashier's check scam. And they get your stuff, too. But then I stumbled across the new variation: rental scamming. They're hunting Craig's List for people trying to rent rooms/apartments/houses.
The con goes like this: the potential renter is in a foreign country (Russia, England, Italy, and African nations are all popular). They are: a college student, going on sabattical, a visiting engineer, international model, etc. (My personal favorite is Carmen SanFrancisco, the International Model from Tempe, Arizona -- currently in Africa, who doesn't speak very good English.) They will pay for several months to a year's rent *in advance* by one of the popular payment options listed above. But oops, their father/uncle/cousin/solicitor sent you more than they intended. It was supposed to be covering their move, plane tickets, etc. as well as rent, and they sent you the full amount. So could you please send them back the accidental overpayment by Western Union? Yep, you guessed how this all plays out. Their international "rent" payment bounces, while of course the Western Union refund goes through, and the money is long gone by the time they stop responding to email. Never underestimate the nerve of scammers.