One of the most important rules of the Uniform Standards of Professional Appraisal Practice (USPAP) is: It is unethical for an appraiser to accept compensation based on the value of a property. An appraiser may accept compensation based on the value of a property only if the property was built after 1990. An appraiser may accept compensation based on the value of a property only if the property was built before 1990. An appraiser may accept compensation based on the value of a property only if all parties agree