This is competely hypothetical situation - really! I was just fantasicing about an easy way to come into lots of money, and thought of this scenario, but then I got worried about whether it would be morally right to profit from it. I hope I'm not the only one who day dreams about things like this!
Suppose you are at a car boot sale, and you come across a stall where someone is selling something you know to be very valuable for a very cheap price. For example, imagine they have a box of old coins they are selling, and you find several coins which you know are worth at over £1000 each. You ask how much they are, and are told £5 each. The seller clearly has no idea of their value. What would you do? Would you buy them all, or buy all but one and tell them not to sell it, or tell them how much they are worth up front so they can decide if they still want to sell them? Legally there's no problem, you'd be paying the asking price, and there's nothing wrong with buying somehting to make a profit, but what about morally?
I can't decide what I'd do. I'd be so tempted to buy them all, but then I'd feel really guilty, especially if the person was having the sale because they needed some extra money themselves. So what would you do?