Sometimes they are meant to be there. Freshly-placed accounts (no previous rank on the account) are placed in Iron.
If you are winning a lot of games, you will climb slowly, but have much higher MMR than represented by your rank, due to bugs with the system at the moment. @ChrisBrownze linked something related to that. (ex. Challengers on smurf accounts will hit mid-Diamond MMR by the time they are Iron I if they are climbing from Iron IV.)
However, I've personally seen Iron IV 0 LP, seriously negative winrate players in mid to high Plat or even Diamond games. These have been very few and far between, but it has been happening. There's no way with MMR as low as those players should have that they should ever be placed in these games.
The first time I saw it, our Thresh rushed Zhonya's, no support item, into Mobi boots, into second Stopwatch, then Targon's, then sold Targon's Brace for Spellthief's Edge. The skill difference between him and the rest of the players in the game was easily 1400 MMR. He honestly looked like he was intentionally feeding at first, but then I could tell that he was honestly just trying to survive and do some damage once I looked at his profile. He'd not been placed in games above Bronze III prior to this game as far as I could see.
What gives, Riot?