Put coercion and mistake on the table, and the ability to get mutual gains is over

From Markets and Morals by Richard Epstein.

A more technical version of the same point is that we hope for all market transactions to generate Pareto improvements, by which we mean that at least one person is better off after it is completed, and no one is worse off. In a competitive market we can achieve that objective if the rules of the game are fully observed. The transaction between two (or more) immediate parties will generate gains for both that exceed their combined transaction costs, so long as the usual rules for voluntary transactions are observed, with the strict prohibitions against force and fraud for inducing agreements. These could be regarded as moral side constraints, but they flow directly from these definitions. Put coercion and mistake on the table, and the ability to get mutual gains is over. It is for that reason that every defender of laissez-faire has stressed these side constraints.