Electronic markets and web-based supply chain management have improved traditional product development processes by increasing the participation of customers and applying various trading processes between companies and suppliers in a dynamic electronic market environment. A multiagent system is an appropriate tool to implement a product development system in a distributed environment because of its flexibility, scalability, and adaptability. This paper introduces a multi-agent system (MAS) based on market mechanisms to support modular platform design. The agent architecture for the proposed MAS is described, including specific agent roles, knowledge, and strategies. In particular, a reputation mechanism is used to select stable and reputable modules for the platform by detecting and dismissing volatile modules in a dynamic electronic market environment. We demonstrate the implementation of the proposed MAS using a multi-agent development framework and how to use module reputation for selecting a module for the platform. Through experiments, we illustrate that the MAS can be used to design modules in a product platform using the proposed market mechanisms.