Trying to scam me
I was playing a game when, out of nowhere, someone on Steam messaged me asking if anyone else was using my account. He claimed that he had sold a skin "to me" but never received the payment, so he reported me and said my account was about to be banned.
He then apologized and told me to add a certain "Steam admin" so I could resolve the issue.
I already knew it was a scam, but I decided to see how far they would take it. Eventually, this supposed Steam admin asked me to disable my Steam Guard, which is something no real Steam employee would ever ask you to do. I didn't disable it—instead, I lied and said I had. Right after that, he blocked me, probably because he realized I had figured out it was a scam.
I'm just posting this as a warning so nobody else falls for it.