cogadh: Never heard of them myself, but it looks like your basic key reseller. I wouldn't trust them, but then again, I don't really trust anyone other than direct sources (Steam for Steam keys, GOG for GOG keys, physical retailers with clearly labeled return policies).
Fever_Discordia: Not even The Humble Store and Gamersgate for Steam keys? O_o
Humble Bundles, yes (because its for charity), Gamersgate, never (I don't trust them). I've also bought Steam keys from Amazon in the past because... Amazon. The point is, unless it is a retailer with a rock-solid reputation, it is not worth the risk of giving them any personal information. That's why I won't shop at places like Target or Home Depot anymore. They used to be trustworthy, but the data breaches they experienced last year due to their complete negligence ruined that.