It's not that I don't believe you, but there'll be something to it. They wont just give it away for free, it'll be a competition of some sort no doubt.
erm i got a game leaflet a few days ago and it had a list of games then said when you trade in one of these you get Modern warfare 2 half price and call of duty 4 was in there
yeah i had loads, like get gta ballard of gay tony on disc for a tenner if you trade in operation flashpoint, cod 4 etc
or get cod 6 half price if trade in any of the following