How Does a CEX Ensure Fair Transaction Ordering without a Public Mempool?

A Centralized Exchange (CEX) ensures fair transaction ordering using a private, centralized matching engine that processes orders based on strict, predefined rules. The primary rule is typically price-time priority: the best price order is executed first, and if prices are equal, the order submitted earliest is executed first.

This internal, sequential processing eliminates the opportunity for external actors to pay higher fees to jump the queue, which is the mechanism of front-running on public blockchains.