In other parts of the county, Zillow's Zestimates  might be accurately but in the North Jersey area, the public data that they use is so bad that there estimates have to be wrong and they are. Some are much too high but most are very low. I was looking at a house that is listed for $349,000 and in my opinion it is worth about $320,000. Zillow gives it a rediculous range of  $228,975 - $610,600 and from the range they give it a Zestimate of $305,300. When you click on the info tab you get the following disclaimer

"What is a Zestimate?

The Zestimate (pronounced ZEST-ti-met, rhymes with estimate) home valuation is Zillow's estimated market value, computed using a proprietary formula. It is not an appraisal. It is a starting point in determining a home's value. The Zestimate is pulled from data; your real estate agent or appraiser physically inspects the home and takes special features, location, and market conditions into account. We encourage buyers, sellers, and homeowners to supplement Zillow's information by doing other research such as:

* Getting a Comparative Market Analysis (CMA) from a real estate agent

* Getting an appraisal from a professional appraiser

* Visiting the house (whenever possible)"
 
Which pretty much says what it really is - A bad guess. My appraisers will tell you that a good appraisal has a margin of error or 5% either way and when you look at the Zillow results for Bergen County, Zillow says that only 35.3% of their Zestimates were within 5% of the actually sales price.