Independent bookselling is not a field for fortune seekers: Most local stores, whether run by retirees, bookworms or those switching careers in middle age, have some sense of higher purpose.

In 2016, there were 1,244 members in the American Booksellers Association trade group, at 1,749 locations. As of this month, the ABA has 2,863 individual members, at 3,281 locations.