Look into it. Succumb to it. oooOOOOoooOOoooooo.
In most cases that someone could advance on me, I've already observed everyone.

So I have information to go on to know if I'm interested. I'm very happy if someone I'm interested in advances, but if it's someone I'm not interested in, I sort of sigh in my mind and check a clock.
However, when someone unfamiliar to me advances, that's already unnerving (I am polite but very distant toward strangers). I don't like being taken aside by people I haven't examined. Once that's happened though, I do try to assess them as fast as I can, and things basically go up or down from there. The less intrigue or endearment that is accomplished in a given amount of time, the more I ask myself "how do I get out of this?". A stranger also has to go much slower than someone I'm already interested in, because I'm still bunkered in and trying to scope them out.
So a stranger still has better chances than someone I've observered and written off, but they have a tough task, I tell you...