See that little thing marked History?
http://i.imgur.com/bls53Bs.jpg?1
Learn to use it. It shows you what things have been selling for. I bring this up because apparently a vast number of people are unaware it exists, or possibly are just stupid. When something has been consistently selling for 10k+, undercutting that price by 4-5k is dumb. Don't do it. Good god.