From SteamRep, which originally came from Steam Support in response to players being trade banned:
Valve is starting to step up and trade ban users who buy duped items. You can choose not to heed this warning, but it's probably not a good idea to buy anything that you know is duped (especially vintages and unusuals) at this time.
It is recommended that you check the history of any high value item and refrain from accepting items that have multiple instances on a single item id.
Valve is starting to step up and trade ban users who buy duped items. You can choose not to heed this warning, but it's probably not a good idea to buy anything that you know is duped (especially vintages and unusuals) at this time.