I believe this happened once Steam started more strict enforcement of regions. To my knowledge a lot of the stuff were resold keys. Legitimate keys, but not from your region.
The whole region thing is pretty dumb. But it is what it is.
I use isthereanydeal.com usually. But I've sworn off buying games for a while. I haven't bought one in almost two years now. My Steam library is ridiculous and I've hardly ever played any of the games. And at that the handful of games I have played in the past year are easily under 5 hours each.
Times change I guess. Unfortunately I've yet to completely kick the habit of hardware.
Speaking of, better get to modifying that power supply