I was in my local Gamestation yesterday and noticed that they had leaflets at the tills with vouchers on them to get extra trade-in.
I was after a PS2 game so I traded one I already had in for £12 instead of £10 without the voucher. I had bought on the sameday Fifa 06 for £2 at Game and when I went into Gamestation the normal trade-in price was £0.50 but I asked if you could ue the vouchers as many times as you want (1 per transaction though) and they said yes so I got £2.50 trade in on a game that I'd bought for £2. I then bought the game I was after.
Instore only.You do have to write your name address etc on the voucher.