The used and collectible book market is a jungle. Despite the risks, it's very possible to make a profit buying and selling books, and books still represent a fairly safe investment.

Consider the condition of the book, what other used booksellers are charging, and the shipping cost for the item.

I cannot overstate the importance of doing a little research before you buy. A book for sale on eBay is as likely to be underpriced as overpriced.

You shouldn't assume that older titles should have prices comparable to more recent titles (e.g. with very few exceptions, old paperbacks will not be worth the cover price of a new paperback, and previous editions are rarely worth as much as current editions). That said, the fact that a book is old doesn't necessarily mean that it's valuable. This is where research goes in.

Similarly, you shouldn't assume that a buyer cares about an author signature. If the author is unknown the signature is worthless, and if the author signs books en masse at events there's a good chance the signature will not affect the price of the book. Some authors will sign each copy of a privately printed or locally printed book, so signed copies are not worth more than unsigned copies.

There are a few genres of books that are probably worth buying on sight if the price seems reasonable. The following list provides a few examples of books I always buy on sight.

Anything archery-related, such as bowhunting, making bows and arrows, crossbows, traditional archery, archery catalogs, textbooks, pamphlets. I bought a copy of the 1878 edition of The Witchery of Archery at a used book store for $8; that's a little extreme, but I almost always resell archery books for a profit.

Fly fishing, especially fly tying or older trout fishing books.

Anything about hunting around the world, especially Africa and India. Some books about hunting in America are good buys too. Jack O'Connor is one of the more collectible latter-day American hunting authors.

Any unusual fishing books, particularly older titles

Anything about spearfishing. It's a genre of limited interest, and books are still fairly cheap. Very few books on the subject have been written recently so the value of spearfishing books should increase substantially. Vane Ivanovic, a Yugoslav author who wrote from the 1940s to the 1970s, is a name to look for.

My impression is that the price of a sporting book is largely determined by the demand for the book. This is in contrast to the value of most modern first editions (e. g. Stephen King books), which is largely determined by the availability of particular copies (e. g. signed copies), editions (e. g. special or limited editions), or printings (e. g. first printings; the term "first printing" is basically synonymous with "first edition," as few later editions are valuable as a first edition, regardless of printing). These books have broad appeal. After all, who hasn't read a King book? Because many sporting titles are quite obscure (privately printed, for example), they invariably have limited printings. If no one wants the book, the book will not sell, and the market for these books is pretty limited. A price based on scarcity or availability will be largely arbitrary. Of course, if the book is in high demand (e.g. an early pamplet on bow-making), the price will be correspondingly high regardless of the availability of the book. Collectors like me will jump all over rare books in particular subjects and ignore equally rare books in other subjects.

Take two publishing houses, Cordovan (Houston, TX) and Naylor (San Antonio, TX), for example. Naylor probably had larger printings, but the sizes of printings from both houses was similar. (Note: I was actually wrong about this. Naylor published about 10 times as many books as Cordovan.) Cordovan books are about $8 on average, regardless of subject (there are, of course, exceptions). Naylor books are about twice as much on average. The higher price of Naylor books more reflects the greater interest in the subjects they cover (more emphasis on hunting over general freshwater fishing), than the availability of the house's books. One of my favorite Texana fishing books, "Panfishing in Texas" by Russell Tinsley, was published by Cordovan in the 1970s. Although I certainly love the book, the book's value is pretty marginal because few people, unfortunately, are interested in the topic.

More to follow on book condition, places to look for books, describing books.