How to consider the County Appraiser's Market Estimate ?

The answer to this question will depend significantly on where you are located.  Every jurisdiction is free to create unique equations or benchmarks on which to base their "tax assessed" valuations.  Consult a real estate professional in your area to get accurate local information.

In King County, Washington, tax assessed values are currently all over the map as measured as a percentage of market value.  Some properties may sell for less than their tax assessed values, while other tax assessed values represent only a fraction of the property's market value.  This is due to the fact that the King County tax assessor calculates property values based on historical trends, and not on the most recent sale data for a particular neighborhood or even a specific sale of the subject property.  In addition, thousands of property owners are disputing their tax assessed values because prices in King County have declined over the past few years.  This means that some properties may have inflated tax assessed values while others are accurate or even low. 

Historically, King County tax assessed values averaged about 75% of market value.  However, marketplace volitility has changed this number.