Agent-mediated reputation systems provide the necessary decision making support to facilitate the automation of processes, and to improve the quality of services in an information asymmetric e-market. Reputation systems encourage honest behavior and discourage malicious behavior of buyer and seller agents by safeguarding honest participants and by laying a foundation for security through social control mechanisms. In this paper, we propose a reputation system that aims to safeguard honest buyers from rogue behavior by counterparties and deceptive buying peers. It employs reputation functions with attack-resilient parameters based on the e-market parameters like value of the transaction and varying experience of agents.These parameters help to reduce the incentive for dishonest behavior, and to minimize harm in case of attacks by rogue sellers in order to improve the trustworthiness among participants in the e-market.