The nature of the imperfect market shock depends on what assumption of the perfect market is voided. The most important assumption for all markets is the idea of property rights. The free market doesn't just depend on the exchange of commodities, but on the rights to use them in particular ways for particular amounts of time. Markets are institutions that organize the exchange of control of commodities, where the nature of the control is defined by the property rights attached to the commodities. Property rights are the most important because they can have the most dramatic effect on the results, and are thought to be behind the most important causes of market failure.