IMO, the scenario you describe just seems like the wrong thing to do. If you've sold a chip for one price and then find out you could have gotten more for it, well that's just the way it goes. I would never dream of asking for it back from the buyer. That's the chance you take by selling it. However, I believe the buyer has a right to their money back (as long as they send the chip back as well) if they're not satisfied.