Thanks for the review — I’m glad you like our site! Picking up on a few of your observations …

1) Owners can publish their own estimates on Zillow but those don’t over-ride our Zestimates. We’re considering using the owners facts (where we have them) to calculate the Zestimate, but will never allow the owner to “fill in the blank” on the Zestimate.

2) The raw data we use to calculate Zestimates actually does comes from the same county websites that display the GIS data. On a home’s detail page on Zillow you will actually find historical sales and tax data but you’re correct in that we don’t publish the owner’s personal details.

3) We do verify homeownership on Zillow when owners claim their house — it’s not foolproof — and because of that we have a process whereby owners can dispute a malicious claim. We’ve found our site’s users are in fact very well behaved in this area.

Thanks again.