I have a website that offers an online service, and I listed it in one of the city Craigslists. Because of that (free) ad I gained an excellent customer who sends lots of repeat business. The Craigslist TOS indicate that their focus is on "local" things. Will they penalize me if I list the same online service in some of their other city editions?
I have been doing that for a few years now and I have never had any problems... Just make sure that the one post has expired before you run another in a different city or they will think you are a Spammer...
Yeah, you'll be alright, you're just not allowed to copy/paste the same ad. Just phrase it a bit differently and submit to 5 or 6 cities at most. There is nothing worse on craigslist to see the exact same ad in EVERY city.
Another important point here is that after Panda update Google Search only shows top two links from any site at a time. So unless you are in top ten of a site's listing, google will not show your result. It MIGHT show up once the website is visited. In that case you should keep a lookout for new players in the market. Craigslist does penalize you for multiple cities but I am sure you can use Locanto, OlX or Selldude and be fine.