I wouldn't spend money to make a winning team keep winning. If at all you can call something 'fixing', its last year's final where CSK lost to KKR after posting a big enough total. The odds on CSK losing when the game started was pretty low, and when they put up a strong total, it should have gone even lower. So when KKR won, the bookies could have made a killing. But I am not accusing that game, because we had a similar game this season where KKR and Bisla again almost pulled off a similar chase in Chennai against CSK (this time, they lost by 14 runs or so).
Only when teams fluctuate or keep losing do we raise suspicions. When teams consistently dominate, you don't call it 'fixed'.