I have added active links to my ecrater store several times.

They only get removed if they are flagged three times by other users. Most people, unless they are competition, or unless you're REALLY spamming with tons of messages, don't bother and don't care.
I just sold an American Girl doll through my Ecrater store that I'd listed on Craigslist. I put it on with a direct link to my store - buyer bought the doll and an extra outfit from my store also. The hits on the doll went from 20 or so to 56 by the time she had bought it, about 2 days after I listed it on CL.
So it does indeed drive traffic to sites, IF you can keep the message there long enough to be seen without getting flagged.