Different categories within Craigslist have different filters regarding what they block and what they allow through. So that part you kinda have to figure out on your own. But to boil it down, you can get ghosted for 3 different things:
1) Your ad copy - something in the ad not allowed by CL. Could be a hyperlink or domain name you included in the ad. If you're using image ads, well some categories do not allow them. It could also be a picture you are attaching to the ad.
2) Your CL user account
3) You IP address
Most likely it will be your ad copy. You will need to start with a very simple test post - text only with a new IP and account. Then keep adding aspects of your desired ad copy back in until it finally ghosts a post. Then you will know what caused the ghosting.
But plain and simple, if you are using a fresh IP and account then something in your ad copy is triggering the ghost. So we have to find what the culprit is by process of elimination.
Hope this helps