Chivalry MW BETA?

its not showing up in your library, so im not sure what you exactly got.

re add the guy and see if you can get a refund for it.

This might be related to the issue of games not showing up when activated. Perhaps only the beta is showing up and not the main game. Do you have family sharing enabled? Apparently, that's been the cause of this other issue.

Hm, that's odd. When you buy the game you get Chiv and Chiv Beta, Chiv beta being a separate application that lets you play the game when there's a new patch that needs to be tested that alters gameplay. Basically being a guinea pig to test the new patch before it gets pushed to live. As others have said, the game isn't in your library, and I've never heard of the Chiv beta application being able to be traded, or to even be had without the main game, so yea I'd definitely try to contact that person you traded.

Go to https://store.steampowered.com/account/, do you see "Steam Sub 29605" or "Chivalry: Medieval Warfare Beta Early Access Comp"?

If so, both of those only contain the BETA and you've been scammed.