I’m heavily in the “press X to doubt” camp with wintrading being a serious issue. It might be something two dickhead friends do if they happen to match together, but there’s too many factors to make a consistent sting operation out of it.
This thread has some interesting arguments in either direction if you scroll past the OP (OP is shady as hell here). It might be worth a read.
If you do see something fishy, you can report for cheating. Otherwise, a non-participation report should cover anything throwing but not incriminating.