Zillow is a wonderful and powerful tool and has changed the way people buy and sell houses, for many reasons I like Zillow. One reason I dislike Zillow is when I am contacted to sell a house and on my first meeting I'm greeted with the happy seller's Zestimate as their listing price. Zillow can not see inside your house, if you have not updated the avocado green bathroom and still have the 1970's paneling Zillow does not know this. So if all of the houses in a mile radius that have recently sold have granite counter-tops, stainless steel appliances, finished basements, new roofs and maintenance free decks and your home is still stuck in the 1970's it is more than likely not worth what Zillow's Zestimate is stating. The same case can be made, if all the houses in your neighborhood that have recently sold have not been updated and you just dropped 50K in renovations into your house then your house could be worth more than the Zillow's Zestimate.
A Realtor takes the time to pull similar home sales within your area and adjust the price up or down based on style of home, square footage, lot size and general overall condition. Your Realtor then can provide you with a solid price range to list your house at, ultimately the listing price is your decision.
Look at your Zestimate but then keep an open mind when you meet with your Realtor as to where to price your home so that it sells for the highest price in the shortest amount of time!