In the library, books sold are classified into commercial and economic categories. Sales books mainly focus on marketing, sales skills, sales management, sales psychology, sales strategies and other sales-related activities. They can be regarded as a part of business discipline, so there will be a special area or bookshelf in the library of business school or school of economics to store these sales books. In some large comprehensive libraries, there may also be specialized commercial or economic departments with books on sales and marketing. These books usually include sales skills, marketing strategies, customer relationship management, etc., and provide reference materials for researchers, students and practitioners in the business and sales fields. Therefore, selling books in the library belongs to the commercial or economic classification.