The commissioner shall prescribe rules governing the qualification and practice of agents, attorneys, or other persons representing taxpayers before the commissioner. The rules may require that those persons, agents, and attorneys show that they are of good character and in good repute, have the necessary qualifications to give taxpayers valuable services, and are otherwise competent to advise and assist taxpayers in the presentation of their case before being recognized as representatives of taxpayers. After due notice and opportunity for hearing, the commissioner may suspend and bar from further practice before the commissioner any person, agent, or attorney who is shown to be incompetent or disreputable, who refuses to comply with the rules, or who with intent to defraud, willfully or knowingly deceives, misleads, or threatens a taxpayer or prospective taxpayer, by words, circular, letter, or by advertisement. This section does not curtail the rights of individuals to appear in their own behalf or partners or corporations’ officers to appear in behalf of their respective partnerships or corporations.