Selling Game Cd Keys From Ebay.

Ive seen people on ebay sell game CD keys like COD 4 COD 5 etc... for like 12$, how could they afford to make profit ? I mean they must be getting these keys for much cheaper from somewhere else. Anyone got any idea where they can get cheaper keys ?

I personally sell origin games at 50% off ... I got family working for ea who have an admin coupon which gives them 60% off any game ...

Maybe they get them free....

I also have 6 dota 2 invites....i give all away for 5$