Market values are also determined by other economic forces at play at any given time. Prices are traditionally depressed when facing an election year when a Democrat is expected to be elected. People equate a Democrat president with higher taxes, less money in their pay check, etc. no matter how unfair such a generalization is. The stock market sees this kind of pressure every 4 years.
The value of the Dollar is the most recent uncontrolled factor affecting values places on guns and related artifacts. Gun shows that used to see people fly in to this country from Europe, the Mid East, and from Africa to buy American Made guns saw None of those customers earlier this year. Collectors with tables containing 100s of thousands of Dollars in antique guns so NO sales, while table selling " Black Guns", and semi-automatice pistols had lines of people waiting to buy guns. That was back when the Sub Prime Mortgage problems were in the news, and the dollar was taking a beating against foreign currencies. The oil price hike crisis of recent days has affected gun prices, now. However, there seems to be more faith in the value of the American Dollar from foreigners, as some good gun sales are being reported again.
What part of the country you live in, or try to sell a gun in also affects the price you are likely to get, and the amount of buyer interest.
I have a very small collection of pepperbox revolvers I have been trying to sell for several years, but can find no interest in them, locally.
Here, you can't find many Winchester lever action rifles for sale, unless they are replicas, but there was a time when a trip through Northern Wisconsin or the Upper Pennisula of Michigan and stops at any gunstore would find racks of original Winchesters for sale, many in better condition than you should have expected. Certain brands of firearms are often found in certain areas, but not others.
My advice is to use the Blue Book Values as a " suggestion", and then visit as many gun shows as you can to see what price others sellers are putting on similar guns. A lot of gun show prices are " inflated" and are referred to as " Trading " prices. IF you are paying cash, you can often get a much better price, particular on the last day of the show!