The CMA relies on vague market trends. The appraisal relies on specific, verifiable comparable sales. In addition, the appraisal looks at other factors like condition, location, upgrades, lot size, house size, etc. A CMA delivers a ''ball park figure.'' An appraisal delivers a defensible and carefully documented opinion of value.
But the biggest difference is the person creating the report. A CMA is created by a real estate agent who may or may not have a true grasp of the market or valuation concepts. The appraisal is created by a licensed, certified professional who has made a career out of valuing properties. Further, the appraiser is an independent voice, with no vested interest in the value of a home, unlike the real estate agent, whose income is tied to the value of the home.