I think the only litmus test necessary is that the account name use the companies name in someway. i.e. If your company is Acme Anvil Co and the terms Acme or Anvil are in the username (or vanity url, etc), in someway, then it qualifies as a business account. Barring that, any social media accounts should be viewed as personal, even if the following amassed under that account came by virtue of employment with the company in question.