This article is by Kenneth Harney, respected real estate columnist. Many Realtors have to contend with the inaccuracy of Zillow’s Zestimates every day when interviewing sellers who believe their properties are worth more than the market value, because they believe the Zestimate they saw on the Zillow website. Also, buyers are duped into thinking they can purchase certain properties for less money than the market due to erroneous Zestimates they have seen online.
In my experience, these Zestimates vary widely from area to area, sometimes too high, sometimes too low. This article sums it up pretty well, showing that the true value of a property can vary from $40,000 to over $120,000 from the Zestimates.
This is a validation of the need to contact a true local expert Realtor, whether buying or selling.