Germany's biggest Craigslist-like service recently added a service like this for purchases that are shipped. I sold my previous MacBook using the system and found it really stressful to wait for the buyer to confirm the item. In my case, it was just someone who was a little bit slow and just forgot, but I can imagine abuse in the system. Same thing happens with PayPal buyer's protection.
I can't think of a better system though, to be honest.