I don't know if the allegations in this antitrust are true or not. However, about a decade ago I wrote a paper (https://www.cis.upenn.edu/~sga001/papers/vex-sigcomm13.pdf) discussing all the ways in which ad exchanges could misbehave without such actions being detectable and some technical mechanisms to prevent violations. I recall some colleagues telling me that surely ad exchanges would never misbehave because deviations from honest behavior would affect companies' reputations, and ethical people within these companies would whistle-blow immediately.

I'm really curious to see where the government acquired their evidence (and what solid evidence do they have), and whether it ends up holding up in court.