dupe working in 2017?? i thought its fixed
Very expensive items ( Howls, Dragon Lores, very rare Knives ) that were copied by Valve due to abuse of steam support system faking that their items were stolen/Hjacked .
It doesn't work anymore. Duped items are items that were refunded by steam support after scam or "scam" - in a way of meaning you can lie to support that you didn't trade items on your purpose and it was your friend. Problems of it can be that duped skin reduce price of every piece of that skin, in most cases you will not be able to trade them at the superior traders that want unique collection.
You can't do it anymore, so no problems
Your duped skins won't be taken away if you think that. A problem could be that you will have difficulty trading it with some kids that care about unique item ID's.