Now Archie,

How do you think Queen Anne and Uncle Fred feel now?

As to the obligations of the Auction House. That would be a determination for a court. If the buyer was able to tell by viewing the item, then an X ray may not have been needed. But if your asking me as a lawyer what advice I would give an auction house (or consignment seller such as Tyrus) if they were selling a mega chip (worth in excess of 5k or 10k), I would advise them to get the chip x rayed.

If an auction house sells a stolen item, they can (and have) been held liable. See Nazi Art as examples. Forgeries can come back to haunt auction houses even years later.

That is the best answer I can give you.