I'm inclined to agree with the taxforwriters.com source linked to by the original poster, The Editor.
Usually states don't tax services such as accounting, engineering, lawn mowing, etc. under the sales tax laws. This makes it different from things like garbage bags and backpacks. There are some exceptions.
States may or may not require licensing or registration of businesses. This may be required at the state or local level. The purpose sometimes is to levy yet another tax, and sometimes it is just to keep track of who is doing business in their jurisdiction. Usually there is no need to prove any competency in the chosen field of business. In addition to sales taxes, if any, the net income may be subject to corporate or personal income tax.
States also license certain professions, such as lawyers, engineers, medical doctors, etc. To be granted such a license the professional must prove competency by showing university degrees, letters of reference, etc., and may have to pass a national or state exam. The professional license may also serve as a business license.
Some professions do not need this kind of license, either because malpractice wouldn't pose much of a threat to the public, or attempting to regulate them would be too much of an infringement on liberty. For these reasons, I'd be surprised if any state tried to make writers or religious leaders become licensed professionals (and I'd lump editors in with writers).