Comps, or comparable sales, are what most real estate professionals use to determine fair market value of a property . When a property is located in an area where similar homes have recently sold, you can establish value by comparing the sales price and features for similar properties to your subject property . Major factors influencing your comparison should be structure square footage, lot size, room count, condition and location. You need to see the actual properties to fully compare them, the printed data will only give a rough estimate of value. States served will often only be limited counties, visit sites to determine availability.