Interesting, I have never heard of getting paid after delivery. I have been buying & selling on ebay since 2003, it has always been "don't ship until you get paid" for as long as I remember.
Back then the window to file a Paypal dispute was only 60 days & ebay did not off a money back guarantee. This type of scam has been around for a long time, sellers sell what they don't have in hopes of the buyer missing the window for a dispute. Now that the Paypal dispute window is 180 days & ebay offers money back guarantee (even for sellers who don't offer returns) itxs much harder but people still try do get away with this scam these days.