The MO department of health and senior services is responsible for licensing all septic inspectors and installers in the state. They have a very comprehensive inspection checklist that they require the inspectors to use. The inspection has some distinct differences between what your septic course teaches and what they require. (not that either are wrong, just different).
A MO septic inspection takes me a minimum of 1 hour (assuming I do part of the inspection at the beginning of my home inspection, and begin the hydrolic load test during the inspection. And we charge between 200 and 250.00 per inspection.
If you contact the state, they may provide you with the inspection forms as well as info on getting NACHI training approved for MO CE. (That would be appealing to non-home inspectors too.)
There are two DEFINED types of septic inspections that are recognized and allowed in the state and they both require a license. An EVAUATION (some might call this a “scratch & sniff” or a walkover inspction), and an INSPECTION (open tank, hydrolic load test, etc). They both have specific forms, that must be used, and according to licensing are supposed to be submitted to the State Department of Health and Senior Services for their records.
I’m sure you could do “maintenance” inspection without a license but if you get caught, they could very easily charge you with a misdemeanor.
If a “maintenance” inspection is what is asked for by the client, then I would do an EVALUATION.