This is similar to the Online purchase arbitrator scam in the Auto category and is very common on websites like eBay or Craigslist. Say you just won an online auction for a video camera. It isn’t cheap, so you’re being extremely cautious about checking out the owner. To prove he’s serious and reliable, the seller suggests you deposit the money into an escrow service, qualified as a thrid party arbitrator. But the service is part of the scam, as being one and the same person with the seller.

How to avoid: if the seller recommends Yahoo Finance or MSN Finance as an arbitrator, stay away, there’s no such thing. Scammers use well-known names to make their operations look more official. They simply create fake e-mail addresses, and send messages to buyers confirming that the products really exist.
The victims send the money to the escrow service, thinking they are safe. Use the official arbitrators of the website you’re buying the camera from.