I don’t think that it’s fair to assume things like these as there’s zero evidence that can prove black money is involved during IPL games. Furthermore all IPL player’s, officials are under constant scrutiny and if anyone was involved then they would have been exposed by now, therefore till credible evidence pops up I feel that we should not spread rumours about IPL unless they can be proved.
You are right we can't say about match fixing until its proven. There is no one who speaks against IPL not even the icc since everyone gets his fair share. The ROI will be low if you rely only on legitimate sources like sponsorship, TV rights etc. Big parties need big return on there investment and this comes only with some fixing.