[Sushimitzu]

A random guy joined the trade server, said "Selling medal for hats". I sent him a trade invite with once, he took a look in my backpack, asked if I had a whoope cap, and he would trade it for whoope cap, which I didnt have. "randomly", there was a guy in server selling whoope cap. He wanted me to buy it from him if I wanted the medal, and yeah, he didnt have so much time either so he wanted me to be fast.
I gave a v.hallmark for the whoope cap, and BAM, both were gone.

Happened to me as well. However, what the OP describes here is not a scam - he does not benefit from doing so. He does not have a friend who happens to sell the wanted hat for Buds. He is not scamming, simply because scamming implies gaining. The way OP did it it's just a joke which is debatable.