Zillow zestimate has been a controversial tool that provides varying levels of accuracy as to property values throughout the nation. Luckily, you can find out the accuracy in your state or county. By going to http://www.zillow.com/zestimate/#acc you can see charts put out by Zillow as to the accuracy of their zestimate tool.
For Pinellas County, Florida, 48.8% of houses sell for more than a 10% difference from the zestimate for the property. This could be a sale for more than 10% less or 10% more than the zestimate. This information is based on Q4 of 2015.
So next time you look at the zestimate for you home, remember that the number shown might not reflect the true value of your property. Check with your local real estate professional for your property's approximate value.