How are you sure? Do you have any proof and would like to show it or tell about it?
What is this? It's like you accuse someone of stealing something but instead of you giving proof of their theft, you ask them to prove they didn't steal.
eSports still seem much easier to fix.
Did you actually include Dota 2 in those opinions of yours?
Because people can easily understand most of how sports like soccer/basketball works. But in a game like Dota 2, it's way more complex. Therefore, it's very difficult to fake things in this game without being noticed by others.