finding double die in your pocket change or any error of that fact reminds me of the saying there is always a gem to be found...keep looking
ebay completed listings are the most accurate way for seeing what the coin has gone for recently. Coppercoins.com is useful as a database, but as is the case with most price guides, they are just that; price guides. They are not kept up to date with sales and auctions, they are more or less just a guess and a "guide" to get the rough value of certain varieties, and do not guarantee that a coin specified in a certain grade will command the price it is quoted at.