http://pages.ebay.com/help/policies/non-selling-seller.html
This help site will assist you. I don't think it would be wise to sue the person simply because it will cause you more headache (time and financially) to go through with that process.
So the seller didn't sell you the item... it...
I purchased 2 tickets to a NY Islanders playoff game from another ebay member. Unfortunately, the team did not advance to the next round and I requested a refund from the seller. The seller refuses to give a refund, based on the premise that he did not offer a refund in the auction. I checked...