Someone (usually a friend) who accompanies you to an in-person meeting arranged via Craigslist to provide support in case of anything going wrong (ex: the Craigslist person being dangerous, creepy, or a scammer). The Craigslist Bodyguard can also simply provide moral support or transportation.
Sam: Are you really gonna meet that mechanic from Craigslist? What if he murders you?
John: Don't worry, James is coming as my Craigslist Bodyguard.