Am I missing something? How?
http://www.gamestop.co.uk/AC4Trade
Blockbuster are running this buy 1 get 1 free pre-owned deal:
http://market.blockbuster.co.uk/retaildiscounts/discountdetails.aspx?id=9199&title=buy-one-get-one-free-mixed-games&tab=offers&pageindex=0
I got GTA IV and Episodes from Liberty City. Can either wait on the latter to come back in stock, or you can get GTA IV and Dirt 3 PS3 and sell Dirt 3 to cex, bringing the cost of GTA IV down to £6 then just find another game on the gamestop list for cheap.
I went for the GTA V tradein deal they were running a while back. Got the game on release date and the refund came through, so basically go GTA V for £15, so pretty confident this should go smoothly too.