FTCHater wins this thread.
Still though. You want to know what to say to a girl who asks you if she's pretty, and do it in a "pick up artist" kind of way ie. you want to know what to say that will steer you towards getting in her pants?
Simply smile, not broadly, but genuinely, and ask her "Why would you ask me that?" This will seem a little standoffish no matter how nice you are about it, but don't be too nice -- better to seem a challenge than just sarcastic.
The thing is, if you want to be a pickup artist, you never want to really close off any opportunity to get a shot of ass in the event that you hit a dry spell. BUT all things being equal, there's nothing in any girl's pants that is worth dealing with the fallout of hooking up with the sort of girl who goes around asking people if she's pretty. She's either so insecure and clingy that you will wish you had killed yourself rather than hooking up with her, or she's such a superficial, vain bitch that you'll wish you had killed her.
So, ask her why she asked. If you get the rare one who says, "Honestly, I just like putting guys on the spot. I love it when I guy makes himself look stupid trying to figure out how to compliment me" then this is a virtually guaranteed shot at some quality tail. She's talking to you because she's interested in you -- if you're interested in her, focus on her and close it.
Frank