CL has implemented many ways of combating spam & scams on their website. But as even the owners of Craigslist have said, "We breed the perfect spammer." There is no way to end it all. Think about it, the site gets more 'help wanted' traffic then Monster.com. They get more traffic then most bigger sites combined so that makes it a big target for spammers.
I'll admit, I used to be a spammer of CL personals section. You could've easily clear $100 a day by posting an ad and then sending the auto response traffic to a dating link. Most ads would get 700+ replies alone from one ad. You duplicate that over 10-20 ads and you have more traffic then you'd ever get from any TGP. Then they started Geo IP blocking and it became a hassle to reset your IP after every post, plus you need plenty of PVA's to keep posting.
Check any blackhat forum and you'll see there are still plenty of people making big money off spamming craigslist. If you have the time and resources to do it then $1k a week is not that hard to achieve.
BTW...here is a pretty cool article on Craig's List by Wired:
http://www.wired.com/entertainment/t.../ff_craigslist