ClearChart: Ensuring integrity of consumer ratings in online marketplaces

Abstract

Popular online marketplaces make an extensive use of ratings to inform their prospective buyers about best-rated products in their service. Given a strong inclination among online buyers towards buying the best-rated products, there is a clear monetary incentive to sellers, and in turn to service providers, to unfairly push their favored products at the top of the ratings lists. Due to the centralized nature of these systems, the problem is particularly hard to solve against undetectable attacks by service providers.

In this paper, we propose ClearChart, a transparency-enhancing mechanism to discourage this misbehavior in today's centralized marketplaces. Our protocol employs a novel distributed version of homomorphic MAC along with cryptographic accumulators and digital signatures to protect integrity of the ratings and improves verifiability of the ratings list. ClearChart introduces only a minimal storage overhead to the buyers and sellers, and can also tolerate collusion among sellers, the service provider and a subset of buyers. We have implemented ClearChart and demonstrated its practicality with an empirical evaluation.