Last year, Valve started dropping a hammer on gambling sites selling Counter-Strike items. This week, the same process has begun for Team Fortress 2
https://kotaku.com/valve-says-theyll-start-going-after-gambling-sites-that-1783609659
In a short statement released online, Valve say that following the ban on CS stuff in 2016, āsome gambling web sites [have] started leveraging TF2 items. Today we began the process of blocking TF2 gambling accounts as well. We recommend you donāt trade with these sites.ā
Those sites, like the CS ones, are shady af. Itās a solid recommendation.
