The same photos have been used at least four times in the past to sell Juy 53 derailleurs at prices of $380, $499, $500 and $549 exclusive of shipping with all auctions ending in apparent sales. So either this guy's sitting on a stock of identical NOS Juy 53s or some real funny business has been going on.
There actually have been a few Juy 53s pass through Ebay over the last few years, here's some photos from some of the past auctions:
Kurt Sperry Bellingham, Washington USA
> I have just uploaded an illustration of a rarely seen cable-operated
> front derailleur from Simplex. This was made from 1952 to 1956.
> The enlarged scanned image is from "The Dancing Chain". Except
> for Campagnolo's Gran Sport, most all other front derailleurs of this
> era were still rod-actuated changers.
> Even more exciting to see is a current eBay offering of a beautiful
> New-Old-Stock example of this model - the first one I've ever seen
> for sale! The seller located in Vienna, Austria shows four excellent
> photos on his auction page.
> (The eBay auction number is referenced in my caption for this image.)
> Very cool!