Still not sure I follow - are we talking about codes that have already been redeemed? If yes, was that a request for such codes so they could use them to scam in trades? How does the fooling exactly work?
if the user receiving such code , doesn't put it in the redeem box before sending its part of the trade.
as we said above, it's kinda pointless if the person receiving it, inputs the code , before sending anything, since the code is displayed as used.