But it could be possible to temporarily fake a human out and make them think they had real bitcoin which is all that is required for an effective counterfeiting operation. Eventually the sucker will find out their duped but by then the thief could be long gone.
I like the question, it is forcing us to think about Bitcoin from a newbie perspective again. and @grendel25 has pointed out an interesting scenario, setting up a fake bitcoin network, with fake wallet and all. agreed this would only dupe a newbie who hasn't done their groundwork... but how many Bitcoin newbies are there out there to be picked off...
I can see the new Nigerian scam, download your new wallet from "here" and lets transact.