Component-based software development (CBSD) has gained recognition as one of the key technologies for the construction of high-quality, evolvable, large complex systems in a timely and affordable manner. In CBSD, the development effort becomes one of gradual discovery about the components, their capabilities and the incompatibilities that arise when they are used in concert. Thus, trading becomes one of the cornerstones of CBSD. However, most of the existing methods for CBSD do not make effective use of traders. In this paper, we analyze the required features for commercial off-the-shelf (COTS) components traders, and introduce COTStrader, an Internet-based trader for COTS components. In addition, we discuss how the COTStrader can be integrated into a spiral methodology for CBSD, providing partially automated support for building COTS-based systems.