The Counter-Strike: Global Offensive gambling "scandal" was one of the bigger events of 2016, one that left a lot of destruction in its wake. After letting such activity slide, Valve started taking action against websites and Steam accounts promoting the behaviour. With a void to fill, it looks like these, uh, entrepreneurs have turned their eyes to Valve's other popular, multiplayer game with item trading.
Yes, it seems Team Fortress 2 has become a target for gambling sites, according to a statement from Valve yesterday. The announcement is brief, but pretty much explains everything it needs to:
In July of last year we outlined our position on gambling web sites, specifically noting that Valve has no business relationship with these sites. At that time we also began blocking many CSGO gambling accounts ... More recently, some gambling web sites started leveraging TF2 items. Today we began the process of blocking TF2 gambling accounts as well. We recommend you don’t trade with these sites.
It goes without saying that dealing with these sorts of sites was already bad idea. If you needed any more convincing to give them a pass, Valve's active investigation should be enough of a deterrent... unless you like the idea of (potentially) having your Steam account banned.
Item Trading [Team Fortress]