No person may appear in a representative capacity before the agency or its designated hearing officer 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 the 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 Washington state law;

(3) 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.