Each State has a Real Estate Appraiser Board which licenses and oversees Real Estate Appraisers. In most cases each state also has a searchable database of appraisers. At each state board site you can find information about licensing in that state, file a complaint against a licensed appraiser, review information about becoming an appraiser, as well as a review the state laws governing appraisers and appraisal related functions.
Click the state name to visit that's state's Real Estate Appraiser Board: