Summary: This article analyzes the conditions under which better product quality implies higher or lower product price. In an optimal control framework, I make the following assumptions: The firm sets the dynamic pricing and product innovation policies; product innovation raises quality, which drives production cost, and consumers are sensitive to price and quality. I derive a rule of price-quality relationship that stresses the influence of quality on price through the effects of cost (positive), sales (negative), and markup (positive). This article shows that, while maximizing profit and despite a quality and cost increases, the firm may decrease product prices because of the possibility of generating more sales as a result of combining better quality with lower price. This sales effect solves the puzzle of a negative price-quality relationship. More generally, the sales effect mitigates the ability of price to convey information about quality.