Who is Fiddling with Prices?: Building and Deploying a Watchdog Service for E-commerce

We present the design, implementation, validation, and deployment of the Price Sheriff, a highly distributed system for detecting various types of online price discrimination in e-commerce. The Price Sheriff uses a peer-to-peer architecture, sandboxing, and secure multiparty computation to allow users to tunnel price check requests through the browsers of other peers without tainting their local or server-side browsing history and state. Having operated the Price Sheriff for several months with approximately one thousand real users, we identify several instances of cross-border price discrimination based on the country of origin. Even within national borders, we identify several retailers that return different prices for the same product to different users. We examine whether the observed differences are due to personal-data-induced discrimination or A/B testing, and conclude that it is the latter.