Pat Martinak of Chicago Rare Books shows off a book about the Columbian Exposition. The store has many books on Chicago history, as well as children’s books, books on jazz and blues and more.

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Paul Garon, one of the four owners of Chicago Rare Books, 703 Washington St., knows why the publisher had to recall copies of Rachel Carson’s second book. Pat Martinak, another of the owners, can explain why the copy of “Huckleberry Finn” on their shelf boasts a first-edition cover but very few pages and why a psalm book from 1663 is priced at $500, while a much newer Governors’ Yearbook from 1964 is $800.

As booksellers, they are privy to the vicissitudes and back-stories of many of the more than 10,000 volumes lining the shelves of their spacious South Evanston store. They are happy to share what they know. “We love to talk about books and to welcome people,” says Ms. Martinak.

They are, in Mr. Garon’s words, purveyors of “books as objects.” Many of their customers are collectors who are “buying more than the content” of the books and sometimes visit the store “multiple times a week,” he says. Ms. Martinak says she had always been a reader but learned from her late husband, a collector of books about World War I, that “there are a lot of other dimensions of books besides the content.”

Peeking under the covers can be compelling. Mr. Garon tells how Rachel Carson disliked the binding of “The Sea Around Us.” The publisher acceded to her wishes and recalled the first 100 volumes, turning those “review copies” into a rarity. The slim Huck Finn, Ms. Martinak says, was a “salesman’s sample.” Peddled door to door in the late 1800s and early 1900s, such books held a scant mock-up of the text and samples of bindings from which the customer could choose.

The four partners together represent well over a century of accumulated information about books. Ms. Martinak, who ran a Central Street bookshop called Alkahest from 1983 to 2002, calls herself “a generalist.” Each of the other owners brings a specialty to the business. Mr. Garon is a blues historian who says he presides over “one of the biggest collections of blues and jazz” books in the country. In addition to selling books, he has written several, including some with his wife, Beth. His most recent work, published in 2006, is “What’s the Use of Walking If a Freight Train Is Going Your Way? Black Hoboes and Their Songs.”

A third business partner, Tom Joyce, specializes in books about Midwestern, Chicago and American history as well as in antiquarian books, some dating back several centuries. Ann Dumler, an expert in fine bindings and for decades a dealer in children’s books, offers children’s classics and 20th-century favorites such as the Oz books and the Nancy Drew series.

The four owners, along with a fifth who has since died, ran a book store on Chicago’s Gold Coast from 1998 until 2004, when the rent became “impossible,” Mr. Garon says. They moved then to what he calls their “lovely shop in a shady dell” a block south of Main Street and west of the tracks in Evanston.

The owners buy some of their used and rare books at other bookstores – bearing in mind, says Ms. Martinak, that “condition, condition, condition” is the most important determinant of a book’s value. It is the bookseller’s equivalent of the realtor’s “location, location, location,” she says.

Other books come from people who bring them to the store, a diminishing source since the Internet made it possible for people to sell their own books, the two say. In most cases the owners buy books from these sellers outright. A few they accept on consignment, says Ms. Martinak – like the huge 19th-century books on Egypt they sold last year for $55,000.

Another way of acquiring “collectible” books – those “whose price is more than it was when they came out,” says Mr. Garon – is at auction or, even better, he says, from collectors or their estates.

Since “people are looking for books that aren’t common,” says Ms. Martinak, the number of existing copies is an important factor in pricing. Religious books from the 17th century are widespread, she says, making the 1663 volume in the store’s current collection less costly than the 1964 Governors’ Yearbook. The latter boasts 48 of 50 signatures and a roster that includes George Wallace, George Romney and Otto Kerner and provides “a little time capsule of politics in that era,” says Ms. Martinak.

Knowledge of the rarity of a book “used to be based on a grand inefficiency,” Mr. Garon says, but the Internet now makes it possible to “identify how many copies are really out there.” The revelation that “books you thought were scarce aren’t necessarily” has “caused some prices to fall,” says Ms. Martinak. But when fewer copies turn up on the Internet than the booksellers had imagined, the price goes up.

Ms. Martinak says she thinks the transparency the Internet affords “takes some of the fun out” of the rare book business. She says booksellers spend more time “shopping” for books online and less time buying and swapping stories about them at stores than before, and she misses “the treasure hunt.” Chicago Rare Books lists 800 books on their own website. It sometimes attracts online customers to the store, where they can choose from many more books – and evaluate their condition.

Besides condition and rarity, collectors look for “first editions in dust jackets or fine bindings,” says Mr. Garon. She warns that not every first edition is valuable; value increases with the author’s fame.

She picks up a small book with streamlined Art Deco illustrations. She chooses a few books, she says, for their beauty and a small number of new books for their uniqueness. “I like them all,” she says. In fact, she admits, “I am reluctant to sell. I have been known to sell one book and buy another to keep.”