Acted shady the whole time. I knew from the start. I even told him I knew he was a scammer, but I know the tricks and was only going to do a trade that wouldn't allow him to steal anything. He insisted he was a legit trader but he could barely communicate and kept acting like he was confused. Eventually we agreed for him to trade an untradable item after a week (once it became tradable) because I knew that wasn't risky for me. He even wrote a strange little promise note on Steam.
Here we are a week later. Of course, he unfriended me, and no longer has the item he promised to trade me in his inventory. Big shock. When I tried to re-add him and called him out in a comment on his profile, he made his profile private.
HE IS EITHER A SCAMMER, A LIAR, A TERRIBLE TRADER, OR ALL OF THESE THINGS.