Craigslist is great and it's very safe.
1. Cash only, and look through it to make sure it's real and the right amount is there. Don't go crazy staring at every bill or anything, but just go through it. No checks, money orders, Paypal.
2. Demo it at your house, hooked up to a decent system with a nice-sounding song. Don't have crazy expensive stuff sitting around the room.
3. Craigslist is safe for audio equipment and similar stuff, generally. Things that attract sketchier people include guns (banned on CL anyway), cell phones and similar small electronics, cars, jewelry, etc. Audio equipment is fine.
4. Don't go crazy about telling the person "sold as-is, no warranty, etc." It's Craigslist. They'll understand it. If they turn out not to understand it, then telling them stuff ahead of time wouldn't have helped.
5. Price it at what you want to get on it, or a little higher. If you get swamped with calls, you priced it too low. If you get nothing after a few weeks or a month, you may want to lower it. Don't put "obo" in there obviously, unless you're really desperate.
6. If someone wants to negotiate ahead of time, that's up to you. Don't be afraid to say "these are awesome speakers, and I really can't go lower on them."
7. If someone shows up and wants to haggle then, well, they've already invested their gas and time. I usually just say "no, my price is pretty firm" unless I'm desperate to sell.
Good luck!