I read the news article about how CD Projekt Red objected to Green Man Gaming selling TW3, but don't see or hear anything about the sales on Kinguin and G2A. But surely the latter 2 sites are a bit more "suspect" ?
gmg-key irritation has been clarified as it seems. keys should be more or less "legit" - while still no information on where the keys come from. i would say we don't need an official confirmation from RED for evers single seller on the planet - just don't buy from shady online shops with a bad reputation.
