Mine is pretty accurate ($2.5M), based on recent sales and a couple of solicitations from realtor friends.

FWIW, we have had a high frequency of home sales in the past year, so that might help. I just looked up my previous house (sold 5 years ago), and Zillow is saying $740K, which I am pretty sure is massively overvalued, however the street it is on, and general area, have a fairly low turnover, so less recent data.