[campyfan39]

This has been a fascinating thread. My take is that if someone is selling something and asking a certain price the buyer is under no obligation to educate them on what they believe the actual value is.
It would be totally different if the buyer haggled with the seller or if a buyer tried to convince someone who had something of great value that is was not very valuable.

The Wagner in the old book at the bookstore is much more complex IMO. In that case, the seller has no idea the card is in there and that he is selling the card. Should he have been more diligent about being sure the books didn't contain anything? Perhaps. Yet also if shown the card at checkout who is to say if the dealer wouldn't recognize it for what it was?