Buying/Selling accounts

Is this something that is looked down upon simply. Or is there a punishment to it? I'm not aware of the complications behind this issue.

I played a game today with a player named "", a Diamond tier player. Except that he wasn't. Someone bought the account and used it to play a game. He was very bm. I wouldn't have said anything if the guy didn't say he bought the account 40 games prior to our matchup. Which I think is kind of stupid myself, why admit to something like that lmao.

But anyways, is there some kind of punishment?