I believe they take an average of all the various regions in the country including online sales etc. I have found that many guns here in Michigan sell for more than the Blue Book prices, but in other parts of the country, such as the southwest, that same gun in the same condition sells for much less than it does here. So as many have suggested here already, just use it as a reference guide to get an idea...then always ask more than it is worth if you're selling and offer much less than it is worth if you're buying...