How do you chat up a shy, geeky person?

I've had a few times where I've been with a fairly shy, geekish girl (I love geeks) but I can never read if they're interested in being more than friends with me because, well, they're shy and geeky.

I've chatted to them, shown an interest in meeting up, complimented them and lightly flirted but I find it's hard to tell. None of them have been extremely withdrawn introverts, but they don't seem to show what they think either when I show an interest.

That's due to their nature, of course, but is there any real way of knowing? Wouldn't anyone react reciprocally? Would they show subtle signs, or is no indication just that and they're not interested?

I find that if there's no sign at all then I'll leave it at that, I don't see the point in chasing after someone otherwise and I may as well look elsewhere, yet I'm curious if I'm missing something just in case.