craigslist: fighting spam

obvious scam craigslist knows about. but i was wondering how you would fake a certified funds check. what i didn't take into consideration is that the certified funds check would come from some podunk bank on the other side of the world, and it would take a few days to verifiy. me in my USA centric thought banks can scan a check to make sure there is balance for it to clear (and certified funds are backed by deposited cash you can't get back).