How can I sell undiscovered keys?

[tanvir ahmed]

I want to sell undiscovered keys obtained in challenges. I don't know how to do that. Please help me.

 

[Pajki_a_sztar]

Long answer short: you can't. You have a game activated on your steam account so steam will let you know when you try to activate the second one that you allready own that game so you can use that key to trade but it still can be a dupe.