Well, if you scam someone doing double money, obviously they'll look into it, but it's beyond me whether or not they do anything..
Hopefully not xD, I've scammed loads from that game.
Jagex tries their best to ban the people that deserve it. But there are so many scammers its too hard to catch all of them. Whenever you see a scammer just report them for it.
I've never fallen for the whole "doubling money" thing, Jagex would've made an announcement by now or have it set in their Contract or Terms of Service or whatever. I've yet to see anyone legit double my RSGP.