Ok this actually happens to my friend not so long ago, he is going on a boxing match and he will bet for the heavy favorite, then suddenly an unknown guy whisper to him, that the fight is going to be fixed and he supposedly heard it from the favorite to win, locker room, are you going to listen to that and bet for the underdog.
What's your take?
Depends on how big the said event is.
If for normal and small events, like small competition, small leagues or something along those lines, a fixed match is more prone to happen. There is a chance that the unknown guy is telling the truth or just luring anyone on a trap to loss at the end.
If for big events, fixed matches are quite not likely to happen or just a low chance. It was surely organized by a Central Sports Organization or any related bodies and there are big people and companies
(as sponsors) behind those events that obviously, they can't just be lured to do something illegal. And players involved in that said event does have a reputation to protect and one wrong mistake to participate in that fixed match scheme, they will surely say goodbye to their career. And for let's say, there's a fixed match involved on such big event, it was done professionally and not just via random guy whispering to random people on the venue.
Bottom line: Why should I follow those?