The only way that bookstores can profitably sell books at below-market prices is to get the books at a discount from publishers  Unless bookstores generate a high sales volume, however, they cannot get discounts from publishers
To generate such volume, bookstores must either cater to mass tastes or have exclusive access to a large specialized market, such as medical textbooks, or both
A bookstore that caters to mass tastes or has exclusive access to a large specialized market will have a high sales volume.