Its impossible to tell if something is duped, untill it poofs of course:sad2:
As for the free item, some people quit the game and decide to give away all their items, giveaways can be seen sometimes on these forums as well, this is not a indication of any duped items however.
One day you'll be entering games with your character and suddenly the item(s) will be gone. Basically, "And like that...poof...they're gone". Hence "poofing". Personally I always saw it as a Usual Suspects reference, but that's just me. :hide:
Well, you might want to look at the items you got from freebies.
Those low - mid - high Unqiue items are most probably not duped.
Those Elite Unqiue with Perfect Stats are most probably Duped.
Those low - high stats Runes words are probably not duped.
Those Perfect on Perfect armor stats Runes words are Most Probably Duped.