This I could find support for, I might get a hand cannon but say my friend gets a scout rifle in the same strike, now logically if we were in the same spot we would have both seen it drop, but in the context of the game we each only saw the one drop, but I'd rather have the scout rifle and he would rather have the hand cannon, why couldn't you trade in a specific scenario like that? In every other place though you'd definitely have to deny trading as its not so much a trade as a "you give me something for nothing"