I have the same issue with TRULIA myself. I used to live in Olympia, and am now in the Redmond/ Bend, Oregon area. They have 3 other houses of the same floor plan, less amenities, and smaller lots and a year older, of an average of 30K more than mine. They even have my house lumped in to an area of town where the houses are valued less and sell for less. They dont even have me comped, with the last 3 houses that have sold in my development. I have written to them numerous times, and even called them, to tell them their glaring error. They dont care, and I was told they got thier info from the public records. AND THEY WONT CORRECT OR DO ANYTHING ABOUT IT!
So I decided to call yesterday to the county public records dept. It was interesting info. They dont give, send or have any interaction with TRULIA or Zillow or any of these other sites any info. and frankly are annoyed with these companies. They said they just have web-crawlers that search public records and throw a dart from there with there description and estimates. It is basically a joke, other than to sometimes see what may be for sale or what did sell. Others that have said the oly way to know or what you should even care about is what a CMA from a realtor, or professional can and will give you.