It is hard to say exactly what I would do as I do not know the individual(s). A lot would depend on whether I liked them/him or not.
I know what would have crossed my mind first: "Why wasn't I at that auction with a wad of money?"
If he was still in posession of them when I found out, and I liked him, I would have tried to assist him. At the least I would have pointed him in a direction to find "real" prices/values.
If I didn't like him, I might have tried to buy them myself.
As I read back over this I realize it does not follow the golden rule. I fall short at times. One thing is for sure, were I the dealer, it is unlikely he would get them back irregardless of what a "justice" might say.
As for him seeing what an ass he is or was, he is doing a fine job of showing everyone through his actions.