The Sales Comparison Approach

The sales comparison approach is based primarily on the principle of substitution. This approach assumes a prudent (or rational) individual will pay no more for a property than it would cost to purchase a comparable substitute property. The approach recognizes that a typical buyer will compare asking prices and seek to purchase the property that meets his or her wants and needs for the lowest cost. In developing the sales comparison approach, the appraiser attempts to interpret and measure the actions of parties involved in the marketplace, including buyers, sellers, and investors.

Data Collection Methods and Valuation Process

Data is collected on recent sales of properties similar to the subject being valued, called "comparables". Only SOLD properties may be used in an appraisal and determination of a property's value, as they represent amounts actually paid or agreed upon for properties. Sources of comparable data include real estate publications, public records, buyers, sellers, real estate brokers and/or agents, appraisers, and so on. Important details of each comparable sale are described in the appraisal report. Since comparable sales are not identical to the subject property, adjustments may be made for date of sale, location, style, amenities, square footage, site size, etc. The main idea is to simulate the price that would have been paid if each comparable sale were identical to the subject property. If the comparable is superior to the subject in a factor or aspect, then a downward adjustment is needed for that factor. Likewise, if the comparable is inferior to the subject in an aspect, then an upward adjustment for that aspect is needed. The adjustment is somewhat subjective and relies on the appraiser's training and experience. From the analysis of the group of adjusted sales prices of the comparable sales, the appraiser selects an indicator of value that is representative of the subject property. It is possible for various appraisers to choose different indicator of value which ultimately will provide different property value.

Source: https://en.wikipedia.org/wiki/Real_estate_appraisal