The current way you decide to trust someone before sending them $400 for a card, a watch, a GPU, a pair of sneakers, or really anything you're buying from a stranger on an online marketplace (Reddit, Facebook Marketplace, etc.) is you check their post history, see if their account is old enough, maybe Google their username, and take a shot in the dark. If you're meeting in person, you're going off vibes and whether they seemed normal over text. For most people that's good enough most of the time, but when it isn't, you're just out of luck.
