There is a famous saying that librarians survive on "Books and Chicken". Because I am already in the library I can get most of my magazines, books, dvds, cds, and videos that I want to watch or use fairly easily.
But, a librarians salary does not let you spend a whole lot on things. This means many public librarians bring their entertainment home from their job. I bring several videos and books home every week from where I work. It is natural that librarians become specialists in the things which they happen to like.
My boss orders most of the videos in the collection. I end up ordering a lot of the graphic novels.
This is probably even more true for booksellers. Most booksellers don't earn huge amounts of money, they are doing their job for the love of books. In New England, it is traditional for many booksellers to have their living quarters directly above their shop. They pay down their mortgage and eventually have a piece of property.
Even with the closing of many small bookstores this can still be said to be true. Instead of selling out of a storefront many booksellers sell directly out of their garage or house on ebay or other online services. This was even true before the internet. Instead of having a web site, many specialty booksellers would have a printed catalog of their books for sale which they would send out to customers. The customer would either meet the person to pick up the book or get the book by mail order. I think of mail order having just moved to the internet.
It used to be to find the price of a book before the internet you would look in small catalogs put out by specialty mail order places, auction catalogs where lots and blocks of books were sold. Also there was something called Bookman's Price Index which is a huge reference work by year which lists the price of a book. Then there were various price guides for books, paperback books, comic books, and other books. The standard price guide to comic books in the United States which is most used is the Overstreet Comic Books Price Guide. We have a copy at our library. You would look through these, approximate the condition and rarity of the item and then price it accordingly.
You might also wander around to other bookstores and see how they were pricing books and check their inventory. Sometimes, the bookseller might even buy something which you thought was mispriced by another bookstore. Booksellers are like a giant grumpy fraternity which can't survive without other booksellers.
Now, there is the internet where you can see comparative prices for books instantly on places like abebooks.com. The prices seem to vary wildly when you are looking for books. But, the variations in prices are not just about the item. People often buy from a particular seller paying a higher price, because they are more accurate in grading their items, have better shipping and handling policies, and better customer service.
There is an ambivalent relationship between librarians and booksellers. Because of this relationship, The Friends of the Library are the ones who hold the book sales to avoid conflict of interest. I have known many librarians who have worked part-time in bookstores on the side to earn extra money or just because they are really obsessed with books. Sometimes, I think it is more likely, they are obsessed with books.
It seems there is a revolving door between publisher, librarian, and bookseller. People who publish library books, especially reference books often hire librarians. Baker & Taylor and Ingram the giant distributors all hire librarians to help libraries select which materials to buy.
Now, the bookseller and librarian are spreading into the internet. Google, Yahoo, and most of the big search engines hire librarians to index and tag their databases. With Google and Microsoft building specialty search engines for books it creates even more of an interconnection.
I am writing this as I search for the Secret History of Moscow which I am almost done reading. I wanted ro read it, but I put it down and can't find it for the moment. I'll find it later today and write a review.