I just played against a guy (didn't lane against him but he was on the enemy team) and he actually 1 vs 9'd the match as mid Fizz. Everyone on my team was a bit better than his teammates, aside from our mid of course and we ended up losing with that Fizz going 18/4/x.
I checked his op.gg and the guy never got past gold for the last 3 seasons, never having great win rates or kda's either. This season he is solo carrying 1 vs 9 mid plat matches with ease (70 percent win rate over his last 20 matches), putting up extremely good win rates and kda's on most of the champs he's playing.
It got me wondering if Riot actually punishes people that get their account boosted or if they just let it slide.
Repost since I had it in the wrong section at first
Edit: I also added the guy and he pretty much implied he was boosting the account without full out saying it. Not looking to get him punished, just really curious how they handle situations of boosting