If something is offered for sale by another dealer, however woefully cheap, it's completely fair to buy it because someone who purports to be a dealer, even a regular at a flea market, is assumed to be knowledgeable.

However (and a big "however") a non-dealer does not represent as having that specialized knowledge.

It is a moral and potentially a legal issue to take advantage of someone in so flagrant a manner.

C'mon, Canvas- does the supposition that the 80-year-old widow was affluent have any bearing on the transaction?