youve only got 7 feedback and what, 3 as a seller so its no great shakes to lose the account and start again if you get negative feedback.
Dont want to be wise after the event but have to echo Hadges comments, how long did you let the auction run watching it in your "selling" ebay and not think there was something wrong with it? You can re-edit a listing for as long as its running, I've gone back into listings and corrected typos I missed or added info that I've been emailed about. I even changed and added pictures (sold a frame and original pic was of the built bike so took ones of the bare frame).
£800 sounds way OTT for a 456 with mid-range kit (and no rear wheel?!).
Let us know what you do but I assume it'll be keep the bike, get negative feedback and possibly bin the account?