Persons appearing before the presiding officer in brief adjudicative proceedings may be accompanied by an attorney or other person, but that individual must serve in an advisory capacity only and may not serve in a representative capacity. In formal adjudicative proceedings, no person may appear in a representative capacity before the agency other than the following:

(1) Attorneys at law duly qualified and entitled to practice before the supreme court of the state of Washington.

(2) Attorneys at law duly qualified and entitled to practice before the highest court of record of any other state, if attorneys at law of the state of Washington are permitted to appear in a representative capacity before administrative agencies of such other state, and if not otherwise prohibited by our state law.

(3) Persons otherwise qualified as possessing the requisite skill to appear and expertly represent others who have applied to the agency and have been duly authorized by the agency to appear in a representative capacity before the agency.

(4) A bona fide officer, partner, or full-time employee of an individual firm, association, partnership, or corporation who appears for such individual firm, association, partnership or corporation.