I have used this device when looking for houses with friends.
It’s like $10 and will detect several different wiring faults. I was somewhat shocked at how often it picks up on stuff. What it seems to be is a “homeowner added this addition him/herself” detector. You don’t even need two hands. One of the best gadgets you can get when shopping for a home IMHO.
That and by looking to see if the electrician that did the original house did his screws perpendicular to the floor - you can sometimes tell DIY jobs without even taking a plate off
Not sure if will be of use here - as a switch presumably only operates the light, but you can pretty much bet money that if some of the regular outlets come back with bad wiring - they put the same amont of effort and training in the rest of their work. Some houses are too old and stuff for the three prong thingies.
I still don’t understand AC enough to explain everything - but I know enough to know - just cause it works (gives power), doesn’t mean it was done right. And in some of those cases - when done wrong - it won’t necessarily bother you, but your family might miss you - and it might work for a very long time before hand.