Second-hand products in GDP
Its because the student did not produce any value added in the production of the book. She used the book and then basically transferred it to the bookstore. On the other hand, the bookstore may repair the book and sell it for a \$10 profit.  (the bookstore may be advertising, displaying, and other services). The \$10 reflects this additional value added in the economy in the current year, and is thus added to the current GDP.