We just advice not to. For the items you are trading for from scammers may have been gotten with by fraudulent items. Although the item itself may not have been scammed, the scammed items may have found its way into the trade for the item you are looking for. Would be a shame to get trade bans, item removals etc by Valve once they get caught up with your particular scammer. Any item you can get elsewhere. No reason to let a scammer profit.