Lots of times people don't care what they have and especially if they got it for free they think it's worthless.
A man in Tucson about 10 years ago always bought paintings at yard sales. He would send photos to the auction houses for appraisals. They would invariably send back the news that they where worthless. That is until one day when he bought a painting that turned out to be worth a million bucks.
He said that he even told the people selling that it was worth more than the $200 they had it priced at but they were people closing out dearly departed mom's house and wanted to get back to Michigan or wherever they were from. That is until the story was in the paper then they wanted the painting back and said the man cheated them out of it etc.
On a watch site I frequent somebody bought a $1000 watch for $3. It was in a pile of junk and needed some work. The lady running the sale didn't care what it was and wanted it gone. Now I don't think that this buyer bent over backwards trying to get her to take more money but he said it was worth more than $3.
People have the internet, especially if they are posting on craigslist. Why should we be obligated to tell people that their items are priced too low? It seems that a good part of this website is devoted to people finding good items for cheap. Should we tell everyone we buy from, "I know that you have this McIntosh amp and pre-amp marked at $50, but it's really worth at least $1000."? Or, "Let me check eBay and see what the going rate for these speakers are, I think you have them marked much too low."?
Chad