Hey buddy, I was just skimming over the last few pages and to be honest you have made the CORRECT decision. Put it this way, you're working on something in a month, have yet to get a backup drive and the hard drive or drives pack up! You loose everything. From my experience from when I was in I.T. if the optical drive has failed due to poor packaging and delivery get rid of the computer. You can end up out of pocket in 4 months. Hard drives are cheap yes but can you afford the time to reinstall everything and remake everything you lose?
As everyone has said, look carefully through the refund process with paypal and ebay, follow EVERYTHING to the letter and send the computer back with FULL records of every action you take. Make damn sure you send it back fully recorded requiring his signature upon receipt and make sure you have a full receipt too.
Then wait for the money and buy something like this and be happy:
http://store.apple.com/us/product/FB398LL/A?mco=MjE0NDk5Mw
Or this:
http://store.apple.com/us/product/FB325LL/A?mco=MjE0NDk5Mw
Still powerful, reliable, under guarantee and most of all packaged properly the Apple way direct to you.
But please please please be careful, it sounds like the guy is fobbing you off a bit with his BS about the hard drives. I really don't want to see you end up bitten.