I do remember there being a problem with match fixing mentioned from several Chinese teams in the past but not from the South American side. Maybe only because they did get caught after those qualifiers were finished. So it wasn't such a headlined story.
If your source is so trusted then could you specify which of those teams were caught after their matches?
These teams were not caught. They will keep doing this. Every match envolving these teams, had a script. Where it be finish a match under x-Minutes, map winners or even under x-kills.
The teams in TI qualifiers were:
Hokori
Red Hot Chilli Pibbles
Lindorfitos
RisingRage
Estar Backs
x5 Gaming
All of the teams above were matchfixing.
On the EWC closed qualifiers there was also
Team Dk
Zetta games
Chandogs (also cheating)
Chandogs on top of matchfix, were also cheating. There was also a rumor that Hokori pos4 "Asao" was also cheating, but i don't have actual knowledge of that one, unlike what i said above.
And yes, Chinese region was devastated by matchfix before. After DPC finished, Chinese and SEA region became infested with matchfixing. Some of those teams are still competing to this day because they were not caught yet. Some notourious examples are the guys from Direborn and Yangon Galaticos, that competed in this SEA qualifier. There's also an infamous stack of players that lost in open quals "cincai team". Those tier 3 tournaments SEA/China, that happen from time to time are 100% scripted. And right now, there's Nemiga matchfixing at EPL. This is why i stay away from betting in anything other than tier1 Dota.