In Zillow's own words they tell you the following:
The Zestimate® 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 calculated from public and user-submitted data, taking into account special features, location, and market conditions. 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
In Zillow's own words they tell you the following:The Zestimate® home
"Our single son lived in the area and we encouraged him to buy instead of renting. He had little experience and we live states away. Angela Niece was exceptional in communicating with us and our son. How often does a 25 year old make this type of commitment? Joes communication, responsiveness and experience were a great fit. I would highly recommend his services. "