I have evidence that they are both high and low (but usually high). I’ve had many Loan Officer’s using Zillow in their intitial conversations with borrowers. But we’ve found that degree of inaccuracy is not suitable to a good prequalification.
As a mortgage broker for over 10 years, I can tell you for fact that Zillow is a poor chice to find home values anywhere in the country. The numbers are simply inaccurate.