yeah, hm... Usually I try to get a feel for the person first based on body language and what I already know about them. I watch the way they carry themselves, what their eyes do (are they focused or dreamy most of the time), if they seem to notice things or walk around oblivious, etc. Then I listen in on their conversations with other people. Finally, if I think I have it narrowed down to a few types, I might strike up a conversation about anything and see how it goes. Typing, to me, is the whole package. It's never about something someone said or how they answered a specific question. But as time goes on, with more and more interaction with said person, it *usually* (not always) becomes apparent. But types are different and little details can throw you off if you focus too much on them.
If I suspect a person is beta, I will sometimes say something a little eyebrow-raising and see how they react. If they laugh, if they eat it up or if they narrow their eyes, those can be clues. haha Bait them and see! If I remember correctly, mercutio is pretty good at that sort of thing. Testing people to get a reaction. It doesn't always give you perfect information but it's fun.