On Craigslist, you can't even list gun accessories, anything with 'gun' in the name, or anything that might be considered as a gun in any way. So paintball gun? Better call it a paintball "marker" (the proper term, anyway.)
Cell phone holster? Might get flagged just for using the word "holster".
I won't shun eBay or Craigslist, I have other hobbies where those two sites are basically the main methods around; but I am a big fan of Gunbroker.