Comparable Sales Used by Assessors Are Stale, Cherry-Picked, or Mismatched
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Assessors determine property values primarily through comparable sales analysis, but the 'comps' they select are frequently problematic: they may be 12-18 months old in a market that has moved 10%+ since then, they may be from a different micro-neighborhood with different school districts or crime rates, or they may compare a 1960s ranch to a 2010 renovation simply because both have three bedrooms. Homeowners who want to challenge the comps must find their own, but they lack access to the MLS data that real estate agents use, and public records are often months behind actual transactions. The structural cause is that assessors are required to value all properties as of a fixed 'lien date' (often January 1), using sales data available at that time, but property markets are hyper-local and fast-moving. The assessment methodology was designed for a slow-moving, data-poor era, not for a market where Zillow updates estimates daily and a home's value can shift 5% based on which side of a street it sits on.
Evidence
Popp Hutcheson's guide to identifying assessor errors specifically calls out stale or mismatched comparable sales as a top valuation mistake (property-tax.com). Matthews & Matthews documents cases where assessors fail to account for lot size, location, and sale date differences in comps (destinlaw.com). Paramount Property Tax Appeal lists 'incorrect comparable properties used' as a primary ground for appeal in California (paramountpropertytaxappeal.com). The Missouri Tax Code (per Uthoff, Graeber, Bobinette & Blanke) allows appeals on grounds that comparable properties were not truly comparable (ugbblaw.com). Avalara's property tax guide confirms that assessors may use comps that don't accurately reflect a property's unique characteristics.