You shall know him by his fruits.
Here is something. Say something really gay. Either a joke or a comment, and watch the reaction. Superficial reactions means they are hiding something, usually.
I had this one gay dude say this to me, "oh yeah, I just want to piss on your face." Now, that is a prime example of a remarkably gay comment. It can't get any gayer than that. Let's just say I turned things into faery dust, for the bad.
You can also make a magickal coin, and use it for divining things like this.