Your title is a bit ambiguous. Would you try again, but this time do it like not everyone is a mibd reader?

How are you defining "opened"? Like the game is running? Or added to your library? And trading games? Like thru the trading system? Valve curtailed that quite a bit, so I wouldn't expect much. And definitely you won't be able to move games to another library. The game licenses aren't transferable.

And then watch Steam sales never happen again.

Publishers, developers, and Valve want people to buy games as that's how they make money as a business. Trading games eliminates any potential profit from new players. Even a game on sale for 75%-90% off still makes more money for everyone involved vs someone trading a game to someone else.

Originally posted by Gorgonsola45:

Be able to trade games already opened...

You buy a license for the game and it's one use only.
You have nothing to trade and don't hold your breath for that to ever change.

Valve cannot legally do this for any game they do not have the rights to. Which is 99% of the games sold here.

The license sold by the devs is not allowed to be transferred to another account for any reason.

Same question every time.
What's in for Steam and the developers to have a competing marketplace next to their game store?