Sold my 3GS on CL for $300 to upgrade to 4.
1. You're going to have a bunch of annoying emails to filter through. Cut down on this by setting a firm price and payment terms, and that you'll ignore any communication that deviates from that.
2. Public place meeting. My meeting spot is in front of a police station, which cuts way down on the scumbag factor.
3. If you get a bad vibe...don't deal with them. Easy enough.
It takes a little effort, but not a big deal. Took me a week, ignored lots of emails, although I was a little tempted by the prince that wanted to buy it for $700 as a birthday present for his daughter. : )