In what game do you mean by that word 'often'?
Not specifically a certain game, but in general.
I don't know about the other games but I'm pretty sure that in Dota 2 and CSGO the percentage of fixed match is small especially if its big tournament or atleast minor tier.
How are you sure? Do you have any proof and would like to show it or tell about it?
I still think that fixed match cases in esports are way less than sports, based on two games that i mentioned before.
eSports still seem much easier to fix. In a real match where players are sweating and beating each other up, primal emotions become more obvious, impulsiveness and anger often fuel a player to forget his promise to the bookie to lose the match and may end up doing something rash which may lead to a win. Chances that the big whale who paid the team to take part in fixing ends up going South.
Thats what I have felt in game, but play acting is also possible so you may have a point worth discussing too.