Guarantees of authenticity for ancient coins ARE available, but as far as I know, such guarantees are only provided by the dealers and auction houses that sell the coins, and not by any third party experts or grading services. For example, here is the explicit guarantee provided by NAC in its Terms and Conditions: Note that this guarantee is unlimited. In the event that one of your heirs discovers 100 years from now that the coin is a forgery, NAC will refund the entire purchase price (assuming they're still in business). Most, if not all, of the dealers on VCoins also offer guarantees of authenticity. You can buy from these dealers and auctions houses with absolute faith that, if the coin is at some point determined to be a forgery, you can get a full refund.