Grav,
Well, it depends who I want to get laid by. I'm cute, sure, but I'm also androgynous and punkish and have hairy armpits (etc.), so I'm not the type of girl who dudes at a sportsbar tend to hit on - which is fine, because I'm not looking to date jocks. I have an awesome boyfriend that I'm in an open relationship with, so I get laid pretty much every day and therefore only post to Craigslist when I'm looking to fulfill a particular fetish - like, uh, ridiculously huge cocks.
It's pretty easy to tell cut-n-paste replies from genuine ones. Real ones tend to respond to what I've said in my ad, while fake ones tend to list all their attributes along with a generic "saw your ad on Craigslist; you look great" type of leader.
Being female means that all of my Casual Encounters ads get flagged within hours, which I once made a post about here. Men are so used to seeing fake ads that they just assume any biological female looking for sex has gotta be a spambot. I find it hilarious that they'd think I was one, though, because no spambot in their right mind is gonna be like "Well, I'm an AA cup and unshaven and I have short brown hair and a little belly." They're gonna go straight for the least-common-denominator T-n-A tall blonde cliche in the interest to attracting as many dudes to their porn site as possible.