Nasty, did you read the fine print
Get Key Codes are free downloads of Bioshock Infinite (PC Game) and Crysis 3 (PC Game) accessed through the Steam online gaming platform when you buy...
EDIT: Actually it's in the terms of agreement
that you can't sell the keys. So yeah, I'd avoid the trouble. Just give them to a friend.
Sales of Key Codes from a participant to another party are prohibited, and may void the Key Codes and/or the Participant's (or third party's) ability to download the Free Games or use the Key Codes.