They shouldn’t be selling products because it creates a conflict of interest. Consulting firms are hired to bring tools into a business that the business doesn’t have or can’t afford normally. They bring experience and skillsets that enable real change and shine light on issues in the company that sometimes can’t be seen by anyone but an outside party.
They also bring the ability to tell it like it is without fear of reprisal, because they are an outside agent hired to come in and do a job. Good consultants should have broad experience and up-to-date market intelligence that lets them look at a clients current process and agreements and make suggestions to improve their results.
Having finders-fee based relationships and commission-based income from vendors and service providers makes you a broker at best…not a consultant.