Another thing I figured out a couple weeks back (took me a while to find this thread, too): the number of negs does not depend on your rating of the girl - it depends on how she views herself.
I was out having a smoke with my wing, and just to keep the ball rolling we opened a girl standing around. She was, honestly, a 6 at best, but must have thought she was a fucking 10. Ego the size of a planet.
So things weren't going on very well and she clearly got the wrong idea we were trying to pick her up. I lit a cigarette for her and she said something along the lines of
'I bet you carry a fancy lighter to impress girls, huh?'
What the... oooh, I get it now, you think you are the shit, little girl? Let's see if that works
[Ace - ignoring the previous remark completely] Say something again... No fucking way, your nose wiggles when you speak! Awesome! (I touch it) haha, it's so squishy! You're cute, like a little bunny chewing on a carrot... Anyhow, Diamond, remember the moves that salsa instructor was showing us earlier on?
She opened up after that and started talking about how self-conscious she was about her nose. Not that I gave a flying fuck, but I think you will occasionally get situations where an 8 thinks of herself as a supermodel, and although you don't think she deserves it, you will need to throw a couple extra negs in there.
Calibrate for her ego (which you should have a good idea of by the time you finish your opener), not your subjective rating of her.