*CBHVAC* writes:

But I am not aware of any cleaning chemicals that require any
license, much less an HVAC (restraint-of-)trade license, so please
cite one by its IUPAC name or CAS number. And be sure to tell us
what governmental authority is enforcing non-sales of this chemical
to us unlicensed folk, like the DoJ and lysergic acid.

The STate of NC. Simple enough. You walk into a supply house here, and
ask for the pretty pink cleaner...or the stuff that looks like cat
****, and before they sell it to you, if they dont know you, they want
to see your state licence...its that simple. The states own law, that
states that non licenced persons can not work, repair, or sell HVAC
products of any sort is enough.

So, cite just one specific chemical that I can't buy in NC.