Steam is pretty active in revoking keys purchased outside of your region intentionally, they have an automated process for finding the activations now. They usually ignore the EU/etc regions who activate in the US just to play the game earlier but they are somewhat diligent in North Americans activating asian keys. People often comment on getting burned buying things on g2keys and etc. The game is a great value from Amazon at $33 or whatever, just buy it there or wait for a sale.
GMG might be a good option still as well, I know they are still running some of those 20% coupon codes.