Agreed that the chief problem of Craigslist as I try to use it is the large number of trash posts. Figuring out a way to filter providers (a la Angie's list?)

http://www.angieslist.com/Angieslist/

would make for a better experience for buyers of services. But maybe that isn't the main business model of Craigslist anyway, so maybe Craigslist is happy enough with the status quo.