You just simply don't trust random people online. I personally would probably never collaborate or invest in someone's project unless I haven't physically met the person, unless that person is actually decently known online and actually has a good reputation.

Also, LinkedIn is pretty much like any other social media site in terms of creating an account. Hence, also easily faked. Don't know why people think LinkeIn is such a big deal. If anything, I'd probably take GitHub contributions and stars a lot more seriously than LinkedIn connections.