Hi
Yeah you do get the light switch booby trap, also underneath bannister rails pointing upwads.
As has been said, they hide them in all sorts of places, any 'dead air space' such as behind baths, tops of kitchen units, behind the sink unit, underneath where the pipes are, in sofas, under them and chairs, in bags, bottles, drawers, wardrobes, discarded clothes, under beds, drawers, wardrobes.
Did a Hep C one (no cure for Hep C) and even though I did 2 thorough sweeps I still came across them as clothes were all over the floor in the bedroom and lounge and they were hidden inside the clothes. Never clean anything out of eye sight (upper kitchen units)
As said each site is unique and any MS/RA will need to be site specific and agree with the cannot gaurentee comlete removal as if by chance you do miss one, then it's your reputation and no one is perfect.
Martin