Whatever patience Valve had with the third-party gambling sites that have cropped up around the Steam Marketplace appears to have finally run out.
In an e-mail to Gamasutra today, Valve's Erik Johnson writes that in the wake of recent controversies over third-party gambling sites that make use of the Steam Marketplace to let players gamble real money on loot crates, Valve will begin ordering the operators of these sites to cease operations through Steam immediately, or else Valve will "pursue the matter as necessary."
The controversy over these sites has extended beyond the rigged, undisclosed sponsored YouTube videos that brought them into the spotlight. Recently the makers of Rocket League said they would not be implementing Steam Marketplace functionality with their new loot crates in order to prevent players from gambling on their loot boxes.
Johnson explains that these sites operate by connecting to the Steam Marketplace in two ways, both of which violate the Steam user agreement. First, these sites use the OpenID API as a way for users to prove ownership fo their Steam accounts, (and request information from Steam users and public Steam profiles), and second, they create automated Steam accounts that make the same web calls as Steam users.
Johnson also says that Valve has no business relationships with any of these gambling sites, which is in response to some site owners claiming they had a relationship with Valve employees.
Incidentally, many broadcast platforms (including Twitch) prohibit users from broadcasting themselves using third-party services in a manner that would violate those services' user agreements or terms of service. That means that Twitch users streaming themselves using these CS:GO gambling sites are technically violating Twitch's own terms of service.