Recent surveys on e-commerce sites confirm the increased use of the Web for shopping. The reasons of these trends have been attributed to different factors such as convenience, saving time, absence of sales pressure, among others. However, an essential site characteristic that should also be taken into account is the quality in use. In this paper, we present a case study on five ebookstores in order to assess characteristics and attributes that influence quality in use utilizing for such an end the Web-site Quality Evaluation Methodology (QEM). The main goal of this work is to show the level of accomplishment of required quality characteristic like usability, functionality, reliability, efficiency and derived sub-characteristics and attributes, regarding the user standpoint. In addition, we focus on sub-characteristics and attributes concerning e-commerce site functionality.