Craigs List does charge for advertising in their most popular local markets in the most popular topic areas like jobs.
Used to be you could post a free job advertising in Seattle, no more. Or, in say Boston metro, but now they charge. But go to a city in South America or to Fresno, and you can still post for free.
The newspapers have had thier lunch taken away from them by CraigsList. They've lost Billions and Billions.
When an area gets too popular, they begin to charge a modest fee.
$25 to $50 for advertising a job. Compare that to Monster, HotJobs or some other career site, and it is a bargin.
I would imagine that CraigsList is an expert at fighting spam, while keeping a very open and inviting format, but I'd think that they must spend 20% or so on fighting spam.
For a free venue, they can't keep that up and I'd imagine that they will do something about it soon.
I've used Craigs List to advertise local jobs for IT Jobs
. It's been okay, but I do get spammed.
Keeping it totally local given them some ability to combat spam, because spammers can only really survive advertising non-local & virtual services like web-hosting, affiliate programs, porn, and the like.