"The seller gets less than the buyer thinks the thing is worth. And the buyer pays more than the other buyers think it's worth."
This sounds like what you're saying is that either the buyer or seller is mistaken about what the worth of a thing is. I don't think that's what you're saying, though.
Perhaps a better way to phrase it is that nothing has an objective "value". The worth of a thing legitimately varies from person to person. So the seller (ideally) is getting more than the thing is worth to the seller, and the buyer (ideally) is paying less than the thing is worth to the buyer. Everyone comes out ahead that way.