Fair market value is a market value of a property it would likely be worth in a deal between two rational, unbiased and unpressured parties. It is an estimated value, predicted, based on reaserch, extrapolation or both. Naturally, it is not a 100% estimation, and can vary depending on the real estate agency performing the estimation. By its definition, the value does not take into consideration factors like personal and sentimental value, as well as any other reasons that are seller-specific.