More of a heads up than anything;
Game have now caught up and are matching any trade in values from competitors within a 1 mile radius.
Thats HMV, Gamestation, CeX, Even ASDA!
All you need is the proof of value (Trade in quote receipt, for example) or some stores may even ring through to other stores to check.
Although Game's trade in prices are alright at the moment, this may come in handy :)