Tohle jsem teď našel:
https://support.steampowered.com/kb_article.php?re f=6748-ETSG-5417#howtotrade
Nic bližšího nevím, o obchodování na Steamu se nezajímám.Does Steam Trading mean I can sell my used games?
No, only games that have been bought as a gift, and thus have never been played, can be traded. Once the Steam Gift is opened and added to your game library, you won’t be able to trade it again.