Governments commonly use proxies for deservingness — tags — as inputs to tax systems. Indeed, presumptive taxes based exclusively on tags are the predominant way that property taxes are implemented. Imperfect tagging can affect the welfare costs of taxation by creating avoidance responses (people changing their tags), but this paper proposes and estimates a novel channel through which imperfect tagging affects the welfare costs of taxation. Imperfect tags generate inequity by over- or under-taxing households, and distaste for this inequity generates behavioral responses that aggravate the efficiency costs of taxation. Drawing on property tax data from Manaus, Brazil, we exploit boundary discontinuities and a reform to its presumptive property tax to assess the impact of the resulting inequities on tax compliance. Our findings indicate a large elasticity of compliance in response to inequity, with values ranging from 0.14 to 0.25, at least as large as the elasticity of compliance with respect to the tax liability. We develop a simple model of presumptive property taxation to demonstrate how mistagging influences the welfare costs of taxation and dampens the optimal level of tax progressivity, highlighting the critical balance between revenue maximization and equity considerations in tax policy design.