How to check duped items

[jadedgeekgirl]

I don't know if anyone has posted this yet, but I found a foolproof guide on tf2pricecheck:

http://www.tf2pricecheck.net/thread-3246.html

If you're trading things of value (bill's, buds, unusuals, max heads, etc) it is imperative that you check an item's history before you sign off on a trade. Duped items are significantly cheaper than original ones, not to mention very hard to sell considering no one wants dupes.

[bunder]

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*shrugs*

[hotlesbianassassin]

basically, look up the item on http://www.tf2items.com/

and see its history. if the history is super-long, it's probably a duped item. check if the item is in multiple backpacks.

example of a duped item. it's on this guy's bp and on this guy's bp.

[jadedgeekgirl]

tl;dr: if it says "this item still potentially exists" in the last category of an item's history, that's a big hint that it's duped. to confirm its status, click on the second to top entry and the first entry. if the original id and level of the item are the same, it's been duped.

[Solarpowered]

More importantly, how do people even dupe items?