I ALMOST fell for this one. I received an e-mail saying that I received a payment to my PayPal account, but would not show under my account on PayPal.com until I shipped the item and responded with the tracking number of the package. I noticed that the e-mail was not from @paypal.com, which was a first clue. I forwarded it to PayPal's spoof e-mail checker, and the dead giveaway was this:

-PayPal will NEVER ask you to ship an item, pay a shipping fee, send a Western Union Money Transfer, or provide a tracking number before the payment received is available in your transaction history.