Gamestation has always been the best for me, although Game next door do occasionally beat their trade in price, despite Gamestation's claim that they won't be beaten.

I've not heard about them 'getting arsey' where Red Steel is concerned. I also doubt they'll refuse to take it. Give it a try - you don't have anything to lose.

You'll probably get around £18 trade in for Red Steel, roughly. I'm not sure about the other game.