Online Course 803: An Introduction to the Sales Comparison Approach to Value. The sales comparison approach uses the market to estimate value by comparing the subject to similar properties that have recently sold. This approach relies on the economic principles of supply and demand, substitution, and contribution. The course begins with an overview of the principles influencing value and moves into methods of collecting data. Referencing sources of market information, the following chapters cover neighborhood, site, and building analysis. Purchasing this course will allow 180 days access starting from the date of purchase. Only the person purchasing the course will be allowed access. You will receive an email after purchase with a link to the course. You may also access the course through "My Account". It is worth 10 hours of continuing education credit.