Property in Maine is assessed according to rules embedded in the State Constitution, Maine Statutes (mostly Title 36), and case law. Local ordinances play no part in the process. Thus the Assessor acts as an agent of the State, although employed by the Town.
These rules direct the Assessor to estimate an approximate market value of each property within the Town. The Town Assessor adjusts values annually in light of the current market; then the state's Property Tax Division audits the work of the Assessor to ensure compliance with legal practices. The market tends to oscillate over time, but as long as properties are valued proportionately, then the system is considered fair.