Valve recently introduced update 7.39e for Dota 2. The developers have introduced a ban on the sale of certain skins.
Items that cannot be exchanged until a certain date can no longer be put up for sale on the marketplace.
Previously, fraudsters exploited a vulnerability in the system and were able to create duplicates of items for further sale. This involved using networks of accounts and bots that carried out exchange and trade operations with each other.
Copying rare skins created problems in the Dota 2 market: as supply increased, the value of goods decreased (items worth $10-25 thousand began to sell for $4 thousand).
It seems that this scheme has been working since the beginning of this year, and in the past months, tens of thousands of copies of items have been created, with damage estimated at $30 million.