How can my house's zestimate go down so far so fast? I have one of the biggest houses on my block??My concern is that Zillow is not gathering info correctly and thus is not a reliable source. The DuPage County Assesor in a writen statement said the fair market value for this home is $423k. I think you need to re-do your algorythm. Question refers to 1300 Palmer St, Downers Grove, IL 60516October 29 200900YesReport a ProblemProblemSelect oneOffensive contentIrrelevant contentSpam (pure self-promotion)OtherDetailsYour emailPlease enter a valid email address.Submit CancelContent flaggedWe will review this content. Thanks for helping make the site more useful to everyone. To learn more, read Zillow's Good Neighbor Policy.We're sorry. This service is temporarily unavailable. Please come back later and try again.