I've always been wary of eBay for something this expensive but CL might serve you well. I would make an appointment to meet the seller at the Genius Bar with the sale contingent on a clean bill of health on the machine. Even if the GB charges you to check it over, it would be worth it in my book.
In addition to the cosmetic appearance of the laptop, if the seller has all the manuals, packaging and cables, it's an indication that the machine has been gently used. Another big plus is remaining Applecare.