Greetings and welcome to the iRV2 forums. Lots of folks with helpful experience post here.
Yes, there are commercial inspectors and they have a trade association:
There have been a number of threads in the past 6 months about inspections and the biggest take-away from them has been this: understand exactly what a particular inspector can and cannot do for you in the situation that presents itself. That means the inspector may not be a mechanic so his/her report will cover the "house" and its systems (HVAC, cooking, water & waste systems, leaks/water penetration, condition of floors/walls/ceiling, side operation, tire dates, battery age, awnings, etc) but nothing on engine, transmission, brakes, steering or suspension.
Depending on the seller you may be able to arrange for a mechanical inspection of the chassis systems or at least have oil, transmission fluid and coolant samples drawn and sent out for analysis.
Is this unit geographically close to you or is it in a distant location?