We study bilateral trade between two strategic agents. The celebrated result of Myerson and Satterthwaite states that in general, no incentive-compatible, individually rational and weakly budget balanced mechanism can be efficient. I.e., no mechanism with these properties can guarantee a trade whenever buyer value exceeds seller cost. Given this, a natural question is whether there exists a mechanism with these properties that guarantees a constant fraction of the first-best gains-from-trade, namely a constant fraction of the gains-from-trade attainable whenever buyer's value weakly exceeds seller's cost. In this work, we positively resolve this long-standing open question on constant-factor approximation, mentioned in several previous works, using a simple mechanism.
@article{arxiv.2111.03611,
title = {Approximately Efficient Bilateral Trade},
author = {Yuan Deng and Jieming Mao and Balasubramanian Sivan and Kangning Wang},
journal= {arXiv preprint arXiv:2111.03611},
year = {2021}
}