There are many cases of casual fixe matches and unfortunately it is difficult to prove it.
Valve stepped down and is giving a very tough sanction for those players and teams that will be proven to be involved with a fix match. They have already made a sample for those players that did it in the past and they're feeling sorry about it because Valve events are the biggest prize pool tournaments that they can no longer participant.
Sample of teams and players that were banned by Valve.
https://liquipedia.net/dota2/Banned_playersEven the virus is spreading the Dota 2 community still continue the major battle and they do this because they want to bring fun to the players but they do this on LAN games only or in the lobby but some of the players is not allowed to travel and connect to the other server and play with their teams so there is a lot of standing on the game but still, they need to adjust because the upcoming international is the thing they need to earn and some of the team does not have direct invited and they need to earn a lot of points to enter into the international 10 so they need to keep it up even they are incomplete.