A Guide Book of United States Coins and Handbook of United States Coins. These are know to us familiarly as the Red Book and the Blue Book, respectively.
The introduction to the Guide Book (Red Book) states that its aim is to give "retail prices figured data from the listed contributors approximately two months prior to publication." In other words, the prices in this source are a composite of the prices at which dealers have been selling their coins. It also describes the reasons why a coin's price might fluctuate.
The front and back covers of the Handbook (Blue Book) boasts that it is the "#1 best-selling book on dealer coin prices." The introduction of this volume reads: "The values shown are representative prices paid by dealers for various United States coins." It also notes that "[o]n some issues slight differences in price among dealers may result from proximity to the various mints or heavily populated centers."
The most important single factor in determining the price of a coin is its condition. Top price is always paid for uncirculated, unblemished coins. These books both detail the varying degrees of condition of coins from About Good (AG-3) -- "very heavily worn" to "Perfect Uncirculated (MS-70) -- the "finest quality possible."
So, to sum up: the Guide Book (Red Book) is the approximate price that the coin dealer will sell the coin to you for; the Handbook (Blue Book) is the approximate price that the coin dealer will buy the coin from you for. Naturally the former price is higher. A dealer will sell a proof (PF-65) 1996 quarter from the San Francisco mint for $5.00, but will buy it from you for $1.75. Thus it pays to look at both books to understand how to get the best price for your coins.
We receive new editions of both of these books annually - our old copy of both of these books in 1953. Having a large range of years can help the collector understand the fluctuation of coin values over the years and also can help an appraiser understand the historic value of coins.
A Guide Book of United States Coins (Western Pub. Co., annual).
Handbook of United States Coins: With Premium List (Western Pub. Co., Whitman Hobby Division, annual)
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