While places that sell new books, such as Barnes & Noble, are called bookstores in American English (bookshops in British English), places that sell old books are best described as used-book stores (or secondhand bookshops in British English). The hyphen indicates that the stores sell used books rather than that the locations are well-worn bookstores. Without the hyphen, the meaning becomes ambiguous; maintaining the one-word bookstore makes the meaning incorrect.