Are you talking about old books or pirated books? Generally, second-hand books are weighed directly by weight. Authentic books generally have bar codes, and books were bought earlier. For example, during the Republic of China, products were in short supply. After the founding of the People's Republic of China, products were scarce for some time, and goods were bought by ticket, but books were bought in RMB before. Now as long as you have money, you can basically buy books that are not too rare.