Two points:
First, it wouldn't be "the best of all possible worlds" if the seller wanted a share of the future increase in value of the chip.
I am not advocating any post-sale adjustments, but if there were post-sale adjustments, the dealer would be hurt by drastic
declines in value and helped by drastic increases in value, so it would not be a win-win (can't lose) situation.

Second, Jim, you are assuming that the dealer gets his chips for next-to-nothing, like out of thin air. Forgetting the time,
advertising expenses, etc., there is the cost of the chip to the dealer. The dealer just might be acting in good faith. Let us say
he thinks a chip is rare and buys it for $850 and sells it for $1000. If the market becomes flooded with the chips and the
prices falls to $300 per chip, what should the dealer do? Refund $700 to his customer and, thus, take a $150 loss (i.e.,
$850 less $700)?