ebay cover-up scam, potentially dangerous. can you work out what is wrong?

thought about it...but will they really care?
Any way to ebay bomb him and leave negative feedback without screwing over my own account?

How about you ask him a question from the link inside the auction asking if there has been any structural damage, dents etc or has the bike ever been in a crash.

If he is feeling honest about then he will respond to the question and add the answer into the listing, if not then he is a douche.