mendoza line. When a fight ends, even if its a win, if you are below the Mendoza line for performance, you get no loot, you are kicked from the raid automatically, and given a deserter debuff. But make it low enough where people who are honestly trying will always exceed the mendoza line.
Maybe that's a terrible idea, I don't know, I don't do LFR. But the majority of complaints I see are about people going in and lolafk during the fights.