This work presents a multiagent architecture that allows a dynamic participation of external buyer agents into an existing multiagent society devoted to book-trading. This work presents an initial approach for obtaining an open MAS system based on dynamic behaviour loading, in contrast to the traditional mediation architecture solutions. Our infrastructure for dynamic participation tackles the conciliation of a buyer agent into an existing MAS covering three levels: semantics, communication and interaction. The PASSI methodology has been used as base software engineering methodology for leveraging the multiagent architecture.