I offer well and septic inspections in all counties except for Macomb and Wayne counties.  These county health departments will have a list of their "Approved Evaluators".
My septic inspection process involves accessing the septic tank and drain field, if accessible, and observing conditions and flow through the system.  It's a considerable amount of work and generally adds 2 hours to the inspection time.  However, adverse conditions can be incredibly costly to repair and often times involve complete replacement of the system.  
The well portion of the inspection is relatively simple, but again, very costly to repair or replace.  I inspect the equipment in the home, the well head and it's proximity to the septic system.  I also place some stress on the system to check it's water production level. 
Water quality testing is not included in the inspection cost but can be lab analyzed for an additional $250 and includes tests for arsenic and lead.  Arsenic is commonly found in water wells in SE Michigan and can be costly to remove from the entire home's water supply.  If you're buying a home with a well I highly suggest having the water tested.