I feel that when a game developer has created such a magnificent game that we feel compelled to buy merch of it, we owe it to that creator to try and let them make a profit from our purchase. They've put the time and effort into making a game that we love, and so we should always prioritize purchasing items where they'll get a share of the money. A lot of the time, fan-made merch won't be officially licensed, and the creator won't have sought permission from the game developer. Of course, it's not always possible to buy from the official website, especially if we're after a particular item, hence why I included both sources.