In the last round of the Candidates of the 2013 World Championship, there were two players left in contention. Kramnik (black vs. Ivanchuk) needed to outperform Carlsen (white vs. Svidler). In the event, Carlsen lost, so Kramnik only needed to draw, but he also had a lost position and resigned shortly afterwards. Carlsen went on to win the tournament and the title.
Now suppose that Ivanchuk hates Carlsen and really doesn't want Carlsen to win. Could he have offered a draw to Kramnik? That would be match manipulation of a sort - he's effectively making Kramnik champion. However I don't see how an outsider can stop him from offering a draw in a winning position, unless they offer him advice during the game ("you're in a winning position! Don't offer a draw!") which should be illegal. Afterwards he can always claim that he didn't think he was winning.
Is there some kind of rule that prevents this kind of scenario? Strictly speaking, a Carlsen-hating Ivanchuk could also have thrown the game ("I just happened not to see that my queen was en prise"), which would've forced Carlsen to win.