Lost Books have always been valuable trophies for Stardew Valley players, as they provide the opportunity to boost skills or gain perks. However, this mechanic now has even more variety with the addition of the Book Seller NPC. Arriving in the game world with the 1.6 update, the Book Seller is a traveling merchant and a great fan of things literature. He will gladly offer you valuable goods in exchange for unnecessary books or sell something from his collection for a decent amount, but finding him is not easy.