Craigslist or Ebay as websites like that have to make money, they aren't paying full retail. Its easier just to sell it there or trade it in at the Apple store (which they do now), as time is worth something also.
Now a days you can use Amazon , Ebay or Social Networks... You can set your own price.
as you says good condition why dont you sell in your own friend and family circle
I have a good condition iPhone 4. I can give it to this website for $115. But I feel like I could sell it for more... Where could I sell it? And what's the minimum and maximum price I could get?