Someone may send you a link claiming that this is a gold generator for Gaia. They may even have stolen the header code from Gaia so it shows the current header with your current avatar to lull you into a false sense of security but even a quick glance at the URL bar reveals that not only is this not a gold generator- it's not even Gaia.
Some may send a link for a grant of a ultra rare-item. You get redirected to a page where you have to log in before claiming it. Just check the URL- it's not Gaia.