Allegheny Pittsburgh Coal Co. v. Webster
In Allegheny Pittsburgh Coal Co. v. Webster, 488 U.S. 336 (1989) the county assessor practiced elective reassessment also known as "welcome stranger," by reassessing properties based on their recent acquisition price while making only minor modifications to those properties that had not been recently sold.
In Allegheny the county assessor's practice violated the Equal Protection Clause of the Fourteenth Amendment. The court held "there is no constitutional defect in a scheme that bases an assessment on the recent arm's length purchase price of the property, and uses a general adjustment as a transitional substitute for an individual reappraisal of other parcels.
The Equal Protection Clause requires that such general adjustments be accurate enough to obtain, over a short period of time, rough equality in tax treatment of similarly situated property owners." Allegheny at 343.