If you insist on getting into the duct cleaning business:
Step 1) Throw away ever scrap of information you have on the over priced glorified shop vac with a spinning brush called a Rotobrush.
Step 2) Look at real duct cleaning equipment that is actually capable of cleaning ducts.
If your plan is to offer residential duct cleaning in an area that primarily has attic installed duct systems, you are getting involved in something that, in all but a very small minority of cases, provides no measurable improvement to system performance or IAQ.
If more government is the answer, then it's a really stupid question.