Like everything, there are many reasons that a value can vary in eyes of the beholder. Especially in today's market where we are seeing a large number of Foreclosures, Short Sales, REOs and regular sellers who are attempting to get a "fair" price for their homes for sale. Unfortunately, depending on who is doing the research, not all CMA (comparable market analysis) or Zestimates or Guesstimates are created equal. One party might take "just your subdivision" while another may take your zipcode ... while another may take your city (picking a 1 mile radius -- for example) ... Then the value is going to be determined by breaking down the search criteria so as to stay within a range matching your Subject House. A Search will be done by Square Footage, Type of Home, 1 or 2 story, number of bedrooms, bathrooms, basement, garage, and the list goes on. Depending upon the "quality" of products used for the interior / exterior and the overall condition of the property ... your value will be critiqued into 3 categories ... High, Mid, and Low (or Cream Puff! Nice Home! or Needs Alot of Work.). In order to do a Fair Market Analysis you will need to have a professional real estate agent come to the house to make the determination of condition and then compare to other homes in your area that best match the Subject Home and then plus/minus the differences. In your case, it would be best to exclude the Foreclosures and Short Sales as they do not fairly reflect the value of your property. Computers are wonderful, however garbage in gets garbage out if you do not have a professional Realtor or Appraiser) physically look at your property to provide a realistic fair market value. If I can help with anything, please call with questions or concerns.