Zillow is worthless, Bad information is worse than no information. You dont need a weatherman to know which way the wind blows, and you dont need Zillow to know its a 500,000 neighborhood. Let it go out of business

Zillow and other Internet sites need to get stuff right before they release their offerings. People don't have time to give sites feedback on what's wrong with them. If Zillow's estimates are wrong, people won't use them.

Hi Brian, it's David from Zillow.

You're right, county tax assessor's have a bias for lower values (typically by 20% to 10%), largely because no-one likes to be overtaxed. We primarily use the recorder's recent sales data as the primary input to calculate the value of the Zestimate. The assessor's data is important though -- the attributes (bed, baths, view etc.) from the appraisal are used to infer the value of the home and to pick its comps from recent sales. When next you encounter a "miss", it could help to note that those attributes can be incomplete -- check whether the home's facts are correct and the basics are complete -- and if not, use the tool we provide to calculate your own estimate using the correct inputs.

FYI - Zillow's accuracy varies by region. Accuracy reporting by state and county can be found here: http://www.zillow.com/howto/DataCoverageZestimateAccuracy.htm

There is no way to tell what the error rate will be for the house you are standing in. No way.

Since an error rate is not known until AFTER a house is sold, how can you know what the error rate is BEFORE it is sold? You can't know.

Also, it is illogical to suppose that just because you know the median error rate in your area, you will know what the error rate will be in the house you are looking at. Knowing the median cannot tell you whether you are in the lower half or higher half of error rates.

Also, think about what a median is. It is just a middle value. (Z will NOT reveal the "average" error rate because it would likely shock you--ask David what that is, he won't tell you).
Anyway,if the median error rate is 7%, half the error rates are below 7% and half are above. First, can you even tell in which half your error rate will be in? Of course not. And think about it. The range of numbers below 7% are 0-7 while the error rates on the half above 7% can be 7-10,000 % or more. Quick example: 1, 2, 3, 7, 10, 50, 1000. The median error rate is 7, the average error is over 150%. That's what Zillow's could be.

Finally, the data, which forms the basis for a guestimate, is not guaranteed fresh, accurate or complete. To publish a zestimate (and use it in reports) when you are missing beds, baths, square ft, rooms, and more, is laughable. Yet that is exactly what zillow does.

Read an interesting debate here with David G of Zillow and decide for yourself.
http://tinyurl.com/uybg6