I witnessed someone who couldn't code fizzbuzz end up at our company (OK it could have been an acquihire or something) then get fired, and then immediately hired at Amazon at a pretty good office. I always had a nagging doubt this person paid someone to stand in for the interviews. Thinking back, who actually cross checks this kind of stuff? Unless they know each other personally or take DNA/fingerprints it wouldn't be very hard to pull it off.