Zillow property valuations are all over the place, and from my personal experience, are too faulty. Most appraisers (zillow's competitors) will also tell you that zillow's numbers don't work for resort markets like ours.
I would avoid any automated property valuations when trying to determine real value.
BTW, Zillow.com recently laid off something like 30% of its work force. Makes me wonder who, or maybe what, will take over there jobs. Will they outsource the work to India? Zillow could give a rat's booty about a property being close enough to the water treatment plant that a person could smell it all day long from their porch. There are good appraisers around here who know how to account for some very local things which zillow totally dismisses.