I have seen after game videos enough where impossible shots were made. Repeatedly.
What is your definition of an "impossible" shot? The problem with most accusations of cheating is that people generally use the term "impossible" to mean "something I couldn't do myself," when the reality is that what is humanly possible goes *well* beyond your own personal limitations, especially if you do not routinely push them. The top tiers of video gaming are full of people who have dedicated their lives to approaching the limits of what is humanly possible, just like the top tiers of any other endeavor you could imagine. Unless you're seeing things like crosshairs snapping perfectly (as in, in zero frames) to unpredictable targets (someone walking in a straight line is not unpredictable), I really wouldn't be that quick to label someone a cheater. There is a very real possibility that they're just that good.
I stand by my assertion that I have never, in 15 years of online gaming, ever seen anyone do anything that I couldn't attribute to pure skill on their part. If anyone I've played against actually was cheating, they weren't doing anything that was humanly impossible, and that I couldn't figure out how to beat.
Furthermore, if you're playing games that a simple automatic cheat could substantially improve someone's play at, then you're really playing the wrong games. Aimbots only help you in games with extremely powerful hitscan weapons, like Counter-Strike (which I've always found boring). Play Quake or Team Fortress. Even if you're cheating, somebody who knows the game better than you will demolish you.