My apologies, I did not realize you were one of those Model X people. I assumed your objections were based in standard socionics, and therefore worth discussing. Won't happen again.
The main thing I look for in V. I. is the gaze. Intuitives tend to have a sort of unfocused and "spacey" gaze, while sensors are more focused on the things immediately around them. Ethical types tend to have a softer, more emotional look, while logicals have a colder, harder gaze.
Mainly, though, it's little things that are hard to describe. Once you've typed enough people of each type, you begin to notice certain similarities between them, and you can sometimes see those similarities in others you haven't typed. Sort of like how some people can tell if someone's been in the military by their posture and general demeanour.
V.I. is really not very reliable. You have to have studied socionics for many years and become skilled at the other methods of typing to be any good at it. It's an interesting place to start, but it's not good enough, in my opinion, to come to a definite conclusion about somebody's type.
The main thing to keep in mind is that at least half of the people here have no idea what they're talking about. It's up to you to figure out which half.