Trading is a system that lets players exchange items with other players. Introduced with the Mann-Conomy Update, this system allows players to swap or gift weapons, cosmetics, tools and more with other players. Later on, Valve also added the ability to trade items from different games to each other.eatures. 1  At first, the Steam Trading window only shows 8 slots to trade. 2  When the 3rd slot on the last line is filled, more slots will appear. 3  This allows for up to 256 items to be traded at once, eliminating the need for excessive trading.