"As is" means buyer beware. It means no warranties of any kind are offered. This is the danger in buying a used car through some method like eBay or Craigslist without taking it to your mechanic BEFORE committing to buy it.
If eBay offers some "Buyback" protection, your remedies would seem to start and end there. You need to review those policies, or hire a lawyer to do it, to see what right and remedies, if any, you have.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Sounds like there was some sort of misrepresentation as to the condition of the vehicle at the time it was purchased. You can always argue that the seller knew or should have known from inspection of the vehicle prior to the time of sale that it had been involved in a car accident, and failed to disclose this to you. That makes them responsible for intentionally concealing material facts about the vehicle. Take this information back to them and demand them to buy it back and give you everything you've paid towards the vehicle. If they do not agree, you'll have to sue them.