Before: Individuals or small groups could attempt to manipulate prices; if they succeeded, there would be easily accessible evidence of them breaking the rules, and they could be punished. Now: Players can anonymously participate in group "buy-outs" of items. The temptation to do so is increased immensely by mob mentality. So now we have more price manipulators than ever that are more difficult to nab than ever. But unless JaGEx removes limits on the Grand Exchange and/or player-to-player trading (or, heaven forbid, they "set" prices), this price manipulation will continue to occur.