The dimensions work out to be 500 gals not 400. The ad also clearly states that it does not leak.
If anyone has concerns just contact the seller and go from there.
Thanks for posting this ad. My parents live a couple of hours away from there. Too bad I live about 36 hours away.
It might not be too bad of a deal, especially if the auction ends without it being sold. Someone that has been in contact with them through ebay email might be able to get a great deal after the auction ends.