According to a recent report from the Seattle Times, Zillow's algorithm overvalued a home in the Seattle area by an absurdly high 700 percent! With an original purchase price of $225,000 (June 2017), the current estimated value of the home in question is somewhere between $268,000 and $318,000 according to other resources. This number, even if inaccurate would fall into the range of acceptable error however Zillow estimated the property to be worth $1.8 million.
At first glance, you might be forgiven to think that the seller's won the lottery to be able to point at a figure like that in negotiations but it really works to their disadvantage. When you Google this home’s address Zillow comes back as the very first search result and that could turn off potential buyers. Even those that do a little extra digging will only come up with a huge margin of error with the pricing of the home and again be turned off.
Can you prevent Zillow from calculating a Zestimate on your listing?
The algorithm is top-secret and based off of thousands of data points which are prone to human error (something that Zillow will attribute to their miscalculations), so the short answer to the question is no. A recent competition was created with a $1 million prize in order to find a coder that can improve the system proving that it is not perfect and it is here to stay.
But there are certain things you can do to improve your chances of having an accurate estimate! Sellers can claim a listing on Zillow and contact customer support to make corrections that may skew the number (such as incorrect amount of bedrooms) but cannot request to change the number itself. Hiring an expert realtor can really help put your listing ahead of the competition and get it sold quickly and (sometimes) for more than asking.