There's been a lot written on how to get the most out of ebay. E-Klasse is right about the pictures. Point out that you are not a dealer and you're selling your personal car. Explain in loving detail all the care attention and garaging you've been through to keep it nice. It should sound special. Make sure you respond to the questions you get and allow them to be posted.
A lot of give and take will help the numbers. Look at some of the other non-dealer ads you like and learn from their verbage and style. Pick one that matches you.
It goes without saying but -- the used car market is soft right now. I have sold a lot on ebay -- and bought my W210 from an ebay dealer, but the best numbers right now are from a quality 4 or 5 line ( not 2 or 3) ad in the highest circulation local paper. In the LA Area it's the LA Times, for example.
The Edmunds(dot)com website has a great forum for setting realistic used car prices based on current market trends and locale.
http://townhall-talk.edmunds.com/direct/view/.ee9c851
Good luck