Steam Community Market
Items can be put up for the amount of money the seller wishes to receive, or the amount the seller wishes the buyer will pay. All items put up have fees added to them: a game-specific fee (currently all games have fees of 10%) of the amount the seller gets and a Steam transaction fee of 5%. Only trusted Steam accounts may use the Steam Community Market. Accounts are considered trusted if they have made a purchase on Steam at least 30 days ago. An account's trusted status will be lost if a full year passes and no further purchases have been made. In order to sell Team Fortress 2 items, a Premium account is required.
The Market is currently limited to Team Fortress 2 Festive weapons, Botkiller weapons, Genuine, Vintage, Haunted quality items and Unusual hats, Dota 2 consumables and invites, and Counter-Strike: Global Offensive items. Untradable items may not be sold on the Steam Community Market.