Let you yes be yes and your no be no. YOU posted it and YOU decided on the price, be a MAN and go through with the deal.
I just had a case on amazon where I had two of the same book listed, one in acceptable condition, one in very good condition. Over the holidays, I had an order for it, didn't realize I had two, and sent the buyer who bought the acceptable condition book the book in better condition. Yesterday had an order for the book in better condition - I spent more than I received from the buyer to buy a book in equal condition to send him.
But craigslist is a completely different animal. No money has changed hands. About 3/4 of people who contact me on craigslist and say they want an item and set up a time to come look at it, never show up. People say they want an item, come and look at it and don't want it, or they don't show up at all. To me, on craigslist, a deal isn't done until money changes hands.