Unfortunately you can never truly know a person online. That's something reserved for being face to face. Sadly the internet is extremely impersonal and gives endless opportunities to be an anonymous pompous *** that can take advantage and abuse others.
However, I'm happy to say I have some very good friends I trust and feel I know as much as my RL friends here on FFXI. You all know who you are, and I'm glad to have you guys around.