Everyone who already has Portal 2 got Portal 2 75% off coupons. They are literally the most worthless item you can have in your Steam inventory. They are specifically given to people who do not need them and therefore people just give them away. No one will give you anything worth month for one of them. Furthermore, the coupon takes $15 off the price of Portal 2. Both games you request are $20. Even if the couple was rare, it wouldn't be worth it. They don't even break even.
