I have indeed, Mr Matrix.
The UKP Community unanimously hold the view that it would be uncool and extremely bad form to try and pull such a stunt, and rightly so.
Even as I posed the question I knew that even if the majority view was pro, ie, (they rob us so why not rob them?), I myself would not feel right doing it.
Yes, there are some tricky WGs who have numerous tactics ( having a fag, chatting on phones, long bathroom breaks etc..) for getting you out the door before time and they're the ones that should be and will be reviewed negatively. There are also many, many decent, honest, fair-playing WGs who genuinely don't mind when we occasionally over-run by 5,10 even 15 minutes past our booking, (God bless 'em) and they're the ones we all love.