I see tons of CL ads by dealers with links to their business websites.
Interesting. I probably should have added - I am by no means a Craigslist "expert," but the experiences I remember were ads and users getting flagged and booted due to external links. Maybe no one is looking at and flagging those ads.
OR, perhaps they are PAID ads. There may be less restrictive rules governing those.
Some verified experiences:
I had an ad selling some paints for a hobby. No external links, just ad copy with allowed HTML and a picture. It was flagged and removed, and there was no explanation. Their message boards were fairly unhelpful, mostly the snarky "sucks to be you" replies, the closest I ever got to an answer was "too much HTML in the ad making it look spammy" (It was a table describing the colors included in the paints) or "wrong category." These paints are for RC cars and aircraft, and there is no fitting category for that, so it was in "Toys and Hobbies." The bozo arguing the point said "paints don't belong in toys."
This isn't a rant, it's to demonstrate the kind of environment you're dealing with. Any registered user can flag a listing. It's like reporting spam, they can flag it if they're in a bad mood, selling competing products, or just not interested in what you have. You're completely at the users' mercy. Enough flags, it automatically gets removed and there's no explanation. All you get is a bazillion references to read the TOS which is loosely defined and generally unhelpful.
I still use it for selling stuff, but personally would never use it to gain incoming links. There's "the way we perceive the workings of the Internet" and there's Craigslist. :-)