The market value of any coin depends on several factors. The first criterion is the intrinsic value of the precious metal in the coin; the second is the rarity of the coin and of course the quality and eye appeal of the coin. Once all of these criteria have been examined the actual current value of the coin can be determined. Never clean your coins to enhance their quality, generally speaking the quality of the coin is lowered by unnecessary or improper cleaning (leave that to the experts).