I now have first-hand knowledge of why eBay and PayPal were two of the first companies to work with Google on their email identity verification system. On Friday, eBay notified me that a MacBook that I had put up for sale went for its full Buy It Now price. Given that the item was for pick up only, I expected an email asking where the buyer could meet me. Instead, my "buyer" sent me a message "apologizing for the inconvenience," but informing me that he would release PayPal funds from escrow after I sent him proof that I had sent the computer to his Pastor's wife in Nigeria.
Two minutes later, an email arrived informing me that PayPal was holding the funds pending proof of shipment. Although a pretty obvious fraud, the email was close enough to have tricked someone who didn't look carefully (or notice the obvious spelling errors). Google's identification program worked as advertised, however, and spotted that the Paypal email was not genuine.
Thus followed a few days of trying to convince eBay to cancel the sale. Today, after my second online chat with eBay support, they finally credited me back my fees. (The computer is still for sale here, if you're interested.)
A bit poor that eBay was so slow considering they must get thousands of these per day. After all, it only cost the scammer one website post, one email and no money!
As I said, I'm a bit skeptical of eBay now. In fairness, however, I was trying to perform an unusual transaction, a "local pickup only" sale. Apparently, the way you stop this scam is to demand immediate payment for "Buy It Now" offers. But this option is not available for local pickup.