Reposting an existing Craigslist ad is pretty simple. Why would you do this? Rather than wait for it to expire, which is usually 30 days, you can repost your ad so that it shows up higher on the results. In some catagories and cities, over 100 ads are posted per day causing your ad to fall down into the abyss very quickly. However, you must delete your old ad or run the risk of overposting and having your account banned for life.