Depends on if the person had to purchase any of the games in the trade or not. If not, then it's fine, but if he had to make any purchases it kind of loses the trade equality of it (from how I'm looking at it, anyway).
My point was in the hypothetical situation where one has a coupon for "$x amount off" and they sell/trade it to somebody for that same amount (wherein the purchaser has to spend money to get the items for trade with the "$x off" coupon).
If the person wanting the coupon doesn't need to spend money in order to get it, then that's fine, it's where they DO need to spend money on it that the coupon loses its appeal to me.
But that's just me, and since I'm not involved in the trade, I'll shut my mouth now :D