When you refer to an appraisal, there are three different sources for that amount. First, the REALTOR will check the multilist for sales of comparable properties near the house that has been sold. In the industry, we refer to these as "comps". They do not go into much depth or analysis and to factor in some differences as was cited such as square footage, lot size, and extra features. Anyone with multilist access can do these. Second is value is called a Brokers Price Opinion. REALTORS, or their boss the Broker, may do these. They rely more on knowledge and experience, but sometimes are not even located in the same geographic area. The last is an appraisal done by a state licensed appraisal. This is the valuation relied upon by the banks or mortgage companies. It is the most comprehensive analysis and costs the most money. Sometimes these people are also REALTORS, but most of the time they are not. The amount of the mortgage is based on their valuation, so most often this is most powerful of the price opinions.