Wouldn't you be able to get a higher price on eBay than on Craigslist? It's also seems a lot safer.
[But then again... I've never used Craigslist but just heard about it]
I tried to sell on Craigslist once, and I got contacted by two different people who said something like "I'd like to buy this item, I really need it, God bless you". It was a very high-quality CRT monitor, and the people buying sounded like they didn't even know what they were buying. I ended up ignoring those emails because they seemed very fake, and since when were CRTs so commonly bought in 2011?
I recommend eBay. Find an iPhone like yours and say "sell one like this". Make the listing very generic, and use a stock photo. Start the auction at $0.01. People get hooked on that and bid it up. My dad and I have done this a few times before, and we always end up selling it for much more than the rest. We sold my dad's 2nd gen iPod touch for $160 in 2012.