Fair Market Value means just that, what willing buyers and sellers are willing to trade at right now.

Any price quote that is not met by a buyer in a short amount of time is too high. Other than lowering your askign price, choices would be to increase the marketing of the product, in this case collectible coins, to try to get the desired sell price, or to wait some amount of time.

The risk is that by waiting, you could actually get even less money if the price falls further.