Before revision:  In this work, we go one step further and show that for many fundamental two-sided markets-e.g., bilateral trade, double auctions, and combinatorial double auctions-it is possible to design near-optimal mechanisms with provable, constant-factor approximation guarantees with just a{\em   single sample from the priors!
After revision:  In this work, we go one step further and show that for many fundamental two-sided markets-e.g., bilateral trade, double auctions, and combinatorial double auctions-it is possible to design near-optimal approximations? Our first contribution is a more general impossibility result stating that no meaningful approximation is possible without any prior information, expanding the famous impossibility result of Myerson and Satterthwaite. Our second contribution is that one{\em single sample from the priors!