<p>Most residential assessors use something similar to Zillow but far more based on local up to date comps put into an equation that produces the value estimate based upon a regression model. It only takes a handful of variables to get a good estimate for the typical homes. The assessment essentially computerized with only a bit of fine tuning by the actual assessor.</p>
<p>If you want a good estimate just pay $300 or so to hire a local appraiser and tell them what the purpose is. They are not that busy right now.</p>