Well-lit and painstakingly organized, Used Book Superstores upend images of the precariously balanced stacks and dusty hardcovers most people associate with used book stores. More than 100,000 new and gently used books—from current bestsellers to staples of the literary world—sprawl across each of the five mammoth locations, which, like so many shattered crates of tea, dot the landscape of the greater Boston and south New Hampshire region. As bookworms hunker down with hardcovers, paperbacks, and children's books, neglected friends can peruse the store's voluminous selection of music, DVDs, and toys, all of which sell for a fraction of their original cost.