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.
I'm a fan of Esports and never heard any of fixed match game, if these cases are true then might as well provide a solid proof that supports your claim even on less known tournament because it will be an Esport scandal that every fan must know. As a player, a hoping player to get better in a game who is dreaming to get into a world stage and show off my skills, selling my gameplay is just another way of me robbing myself.
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.
I have to disagree on you, fixing an Esport game is way harder to do than the other games since it will not only need a single person to fixed the game but the whole team, whole brand of the team including their sponsors. Fixing a game is not a one man job, this already tells us that Esports scene is authentic and true to its passion.
I know several players who cheated on international stage, Esports is not rigged and they kicked them out.