I think I'm going to go with the dissenting view on this one, though I'm not sure if I'm serious or as a devil's advocate.

In the yard sale example, I might operate from a simple principle: I have no moral obligation to do other people's research for them.

It is their item, and they can place it for sale for any price they wish, as that is the prerogative of any owner (unless they're in an actual business and Congress is still in session, in which case they can only charge what the almighty legislators think is reasonable, else it's "gouging." Business owners don't have property rights, but the yard-saler does).

There are facts of life, and the more we shield people from the consequences of poor action, the more it will breed. This is a small-scale version of a type of economic 'moral hazard.' The market will teach lessons that could prove very valuable, in ways that will not be forgotten. It might even be best to buy it at the deal price, and then inform the seller of its real value just before leaving with it. The seller will potentially be better off in the future, and more inclined to figure out what he's doing before he does it.

If you simply inform him of the actual value, and he has no felt loss from the encounter, he is far more likely to forget the moral of the story and continue to do himself harm in the future.

Also, a yard sale is inherently an admission by any seller that they do not particularly want to receive the market value of a product, but that they simply want to get rid of it very quickly and gain a little in the process. To buy at the "deal" price is fully in-line with the purpose of the sale itself.

__________________
Jeremy Gage
First Baptist Church
Durham, NC

"No heart can conceive that treasury of mercies which lies in this one privilege, in having liberty and ability to approach unto God at all times, according to his mind and will." - John Owen