Zillow was created for consumers but it appears to be a guesstimit. Realtors do a Comparative Market Analysis but realize that all CMA'S are not created equal either. A good CMA will compare and add or subtract for every asset/amenity your house has to the subject sold. Westwood Metes & Bounds has been doing CMA'S like that and that is why we are the number 1 selling real estate agency in all of Ulster County for 17 years straight (based on Ulster County Board of Realtor statistics). You can also pay a licensed Appraisor for an Appraisal.