Zestimate

If your home is worth $200k and you believe the estimate is off by $200k, then there may be an issue with data used for the "recently sold" in the area.  There is a place on the home details page to "report a problem" (under the edit pull down tab under the main photo).

Zillow staff can look at some of the issues, but in most cases they cannot do anything about the number.  Also check to see if you have the correct county records details (lot size, living space, #bedrooms, #bathrooms, year built, price paid, date purchased, etc.) as these can affect the estimates.  New estimates are automatically calculated 3 times per week, but there is a delay of several weeks for use of owner/agent revised numbers.

The county tax assessed value is for taxing purposes only, and is not intended to reflect a fair market value.  Not to mention, they are only changed once per year at the most, so they don't take into account other sales in the area.  And since counties need tax revenue, they tend to be more likely to raise the assessed value instead of lower it.

Because the Zestimates are automated, they are calculated using information based on average selling prices in a broad general area.  If you would like a more specific estimate of your home's value, I can provide one for you, free of charge.  I would need a few specifics in order to compare the current value of your home to others that have recently sold in your neighborhood.  You can then make an informed decision about whether or not to sell. No pressure, just information.

Kind regards,
Jean [contact information removed by Zillow moderator]