In this paper, we examine a trust-based framework for promoting honesty in e-marketplaces that relies on buyers forming social networks to share reputation ratings of sellers and sellers rewarding the buyers that are most respected within their social networks. We explore how sellers reason about expected future profit when offering particular rewards for buyers. We theoretically prove that in a marketplace operating with our mechanism: i) buyers will be better off honestly reporting seller ratings and ii) sellers are better off being honest, to earn better profit. Experiments confirm the robustness of the approach, in dynamically changing environments. With rational agents preferring to be honest, the buyer and seller strategies as specified constitute an effective approach for the design of e-marketplaces.