Send copies of the auto trader ad, the EBay ad, and your history with this car, as described above, including the contact information of the previous owner to
http://www.ifccfbi.gov/index.asp , which is a Federal reporting site for internet fraud, and cc: the email contact link at EBay. If EBay is true to their policies, the auction will get pulled and the seller banned from EBay.
If you are really lucky, the EBay seller might even get some jail time!
If not, as least you will feel better because you tried to do the right thing.