Buying a book at the suggested retail price might be a bigger mistake than judging it by its cover.

Flat sales, savvier readers and the emergence of new players in the retail and online marketplace are keeping the pressure on sellers to offer more books at a discount.

Book sales have held steady over the past year. Consumers spent roughly $2 billion on books in August 2009, about the same as August of last year, according to the National Retail Federation, which tracks sales.

Booksellers are also betting customers will buy more than one deeply discounted bestseller, says Scott Testa, an assistant professor of business administration at Calibri College in Radnor, Pa. “Retailers know consumers hate to pay for shipping,” he says. A customer who buys Amazon’s $9 copy of Dean Koontz’s “Breathless” might be tempted to spend another $16 on other items during that transaction to get free shipping on the whole order.