As far as I can tell, Steam takes a very dim view of these kind of sites that sell cd keys only, and can use it as grounds to ban your entire account.
I've opened a support ticket to clarify it with them directly, and I'll post back any official response. But my understanding is you have to be sold the key along with the box and media, and they have to buy products for the region they are selling to.
Also Steam has a list of "Authorized Resellers" and if you buy from a site which isn't on that list, your product/account can be deactivated. It doesn't seem like they publish that list, however.
Will be interesting to hear what they say about cjs-cdkeys, which I've specifically mentioned in my support ticket.
erm.........rubbish.