Item duping.

If you have to do with high value items like Max Heads, Unusuals, Buds you will notice that many people speak of duped items. Those are items that exist more than once and have the same history.

It was possible to do like this: You traded the same items through steam trade and ingame trading simultaneously. Somehow one person will then lose it's items while the other gains them double. (please correct me if this is wrong).

Anyways this doesn't work anymore and I got told that there doesn't exist a way to dupe right now (except staging a hacking attack).

But not too long ago I saw someone dupe an unusual hat. I asked this person but he told that Valve did it (which is bullshit because he had both in his bp). He didn't want to tell me how he did it, but I am sure that there is a new way to do it. Naturally you wouldn't tell it anybody because else everyone will do it and crash the economy. But isn't this site made to share tips and tutorials?

So if anybody knows the new way of duping or has more information on it in general I would like him to post here.

Thanks in advance