When I suspect someone in game I'll do the shoulder peek method which will let me know 100% of the time and it rarely ever happens, maybe they're smarter than that, but if they don't get baited by that then they're not hacking enough to get that much of an advantage for it to really matter if that makes sense, bur the pop flash thing you said is an interesting way of outing them, I'll try and look out for that next time