We don't find them accurate either, as stated below. As an online source, we find Zillow to be fairly accurate in the Tarrant area, but just like Zillow tells you on their website: Buyers, sellers, and homeowners should supplement Zillow's information by doing other research such as:
Getting a Comparative Market Analysis (CMA) from a real estate agent .
Getting an appraisal from a professional appraiser.
Visiting the house (whenever possible).