How to spot an FBI/CIA/CSIS agent in an online community:
1. They have a tendency to imitate/mirror you. This is particularly true when they try to get close to you or try to befriend you. If you find your posting style/diction/sentence structure/sentiments reflected frequently in someone's posts, and you are reasonably sure it's not just some kid looking up to you and who is trying to emulate you, chances are, this poster is a fed. This is especially true if he is highly intelligent.
2. Feds' posts are characterized by lots of style and smarts, but no substance or soul. If a poster is highly intelligent and eloquent even, however his posts do not "move" you, chances are, he's a fed.
3. Feds seem to be biologically incapable of endearing themselves to other, normal people like you and me. If there is a poster who's highly intelligent, however he behaves in a way that just "grates" you in ways you can't quite put your finger on, chances are, he's a fed.
4. Feds are incredibly vulnerable to the Socratic method. They might say something designed to appeal to your sensibilities, however if you press them to expound on it, they either go silent, or try to answer, although almost always in a very unsatisfactory way that gives them away.
5. This is minor, but my observation is that feds tend to be sexually uninhibited or unrestrained in a very unattractive way. They talk about sex more often and more explicitly, in a way that's very off-putting.
6. Feds ingratiate themselves with you, in a shameless and very un-subtle way, to the point of being slightly sickening.
7. Feds do not know how to conduct themselves in positions of power (say, if they are the moderator of a forum). They have a tendency to abuse their authority. I still don't know why they behave in such a brazen manner. Is it because they are so sure of the absolute power they hold over you, or is it because they suffer from a biologically rooted inability to tell appropriate conduct from the inappropriate? Who knows?
Anyway, I hope you guys enjoy my little guide.