Zillow is not an appraiser. It is pretty solid for a quickie overview of prices. It works off of completed sales in an area to give approximates of home values. Of course it does not take into account specifics of that particular home, but in a cookie cutter neighborhood, it is fairly accurate. Actual appraisers are nothing to write home about. Prior to the meltdown, they were over inflating to satisfy lenders and now they are way undervaluing to cover their a$$.
I'm just being snarky this morning. I'll go to zillow when I'm reviewing loan mod cases, just to see if they're in the ballpark.
Having done accounting work for homebuilders for 20+ years, I'm well aware of the games played in obtaining appraisals.