Parity in Markets -- Methods, Costs, and Consequences

Fisher markets are those where buyers with budgets compete for scarce items, a natural model for many real world markets including online advertising. We show how market designers can use taxes or subsidies in Fisher markets to ensure that market equilibrium outcomes fall within certain constraints. We adapt various types of fairness constraints proposed in existing literature to the market case and show who benefits and who loses from these constraints, as well as the extent to which properties of markets including Pareto optimality, envy-freeness, and incentive compatibility are preserved. We find that several prior proposed constraints applied to markets can hurt the groups they are intended to help.