In Reed et al. v. The County Commissioners of Delaware County, Pennsylvania et al., the U.S Supreme Court dealt with a dispute over property tax assessments in Delaware County, Pennsylvania. The plaintiffs were owners of real estate who claimed that their properties had been assessed at full value for taxation purposes while other properties in the county were assessed at less than full value, thereby violating equal protection under law as guaranteed by the Fourteenth Amendment to the Constitution. However, they failed to provide sufficient evidence proving this claim and thus did not meet their burden of proof. The court ruled against them stating that mere allegations or belief was insufficient to establish unconstitutionality; concrete facts demonstrating unequal treatment must be presented instead. Furthermore, it held that occasional mistakes or errors in assessment do not necessarily constitute a violation of constitutional rights unless there is systematic discrimination involved which wasn't proven here either. This case reaffirmed two key principles: first - taxpayers challenging an assessment bear the burden of proving its invalidity beyond reasonable doubt; second - isolated instances of misassessment don’t violate constitutional rights unless they are part of deliberate discriminatory policy.

The dissenting opinion in Reed et al. v. The County Commissioners of Delaware County, Pennsylvania, argued that the majority's decision to uphold a tax assessment on stock held by residents of Delaware County was incorrect and unjustified. They contended that the state law allowing for such taxation was unconstitutional as it violated equal protection rights under the Fourteenth Amendment since it taxed only certain types of property (stocks) while exempting others (bonds). Furthermore, they disagreed with the majority's interpretation of "domicile," arguing instead that one's domicile should be considered their place of residence rather than where their stocks were physically located or managed. This would mean that out-of-state corporations could not be subjected to local taxes simply because some shareholders resided locally. Lastly, they expressed concern over potential double-taxation issues arising from this ruling and believed it set a dangerous precedent for future cases involving similar circumstances.