Libraries and bookstores share one common dilemma: what books to stock and acquire. Of course having said that, their approach is significantly different. Bookstores for the most part are interested in profit and have a better turnover of books. What's on my shelf this month might not be the books you'll see in the store next month. Unfortunately for libraries, that's not the same scenario. Libraries I think should be focused on the long term: what are the books I want on my shelf that's not only going to be valuable this month but for years to come?
Perhaps the biggest problem faced by libraries is that it's searching for a value that's not quantitative. In a bookstore, the books you should carry can easily be measured by your sales. With libraries, that's not the situation; as much as I want to think of it in business terms and imagine that a library will stock books that frequently gets loaned, that's not how libraries are run. Normally, each library has its own agenda, its own set of values. Like the Filipiniana section of a library won't be stocking English books, even if all of its books are unpopular or only catch the interest of scholars and professors. So the first thing to identify is the library's mission and vision, or what it wants to accomplish. Without that, libraries and its staff will simply be wandering in the dark as they amass a hodgepodge of books whose inclusion will ultimately collapse into library politics.
Of course even if the agenda question is solved, the next problem is determining quality. For example, a children's library might be interested in acquiring books for children and perhaps slowly stock some young adult books or even novels that children "should" read. Libraries unfortunately have a limited budget (as do most organizations) and so they can only acquire so many books (and you know, not purchase every children's books that's published for that month). There's also shelf space to take into consideration. When you acquire a book for a library, it's supposed to stay there permanently (theoretically--book thefts and unreturned books must be accounted for after all). If you fill a library completely in the first year, acquiring more books for the next year is moot unless you somehow find the space to store the new books. There are one of two ways to accomplish this: either expand the library or get rid of old books. Some make do with an improvisation of the former, such as adding more shelves instead of expanding your real estate. Those that choose to get rid of old books to make way for the new are faced with a difficult problem of choosing which books to keep. And this is where quality comes in.
Unfortunately, at the end of the day, judging a book's quality is entirely subjective. One can occasionally find guidance through book lists, a school's curriculum, or the Newberry Medal but that can only account for so many books (not to mention that "classics" and books that have won awards are usually contended by other parties whether to censor them or deemed inappropriate). There is no real objective method to determine what books to dispose of and what books to keep unless you want to go into the numbers game (i.e. what books were frequently loaned, what books can't be restored, etc.). And honestly, there is a real value for library to keep "unpopular" books because if a library doesn't keep stock of out-of-print and seldom-used books, who will?
Even if a librarian manages estimate a book's subjective worth, there's the uphill battle of convincing his or her superiors to agree with that judgment. Well and good if the librarian's tastes is similar to their superior's. Or if the superior completely trusts the judgment of the library staff. But in the case of school and university libraries (which unfortunately is the oft-used libraries here in the country), there's probably red tape to go through, a complex administrative screening process involved. And I'm not saying that's wrong, it's the school that's funding the library after all. But it's a situation where the values of a librarian is entirely different from the values of the school administration board and that influences what books are actually shelved and what aren't.
When you see a book in a library shelf, one can't help but wonder what rigors and battles this particular book had to experience to be where it is now. Was it literary novel or a popular book for its time? Did the administration want the book or was it the librarian's choice? What book did it replace or what books were declined to retain it? Every book in the library has a story to tell although it's a story most of us take for granted.