A difficult situation Lee and only your conscience can resolve it.
You deliberately lied on the eBay auction and actually described what had happened.... then later admitted on your other thread that you had 'guessed'.
My friend had the bike before me and came off on those loose chippings that the council put on the roads,,,,if your already a biker youll know how bad they are..He was doing about 20mph and hardly any damage was done
Stating that you bought the bike from your friend and describing how the bike was dropped, would instantly make me suspicious to the fact, you knew the full extent of the damage, although on your other thread you say this 'friend' is only someone you went to school with and hadn't told you. You state 'hardly any damage was done'. I imagine this is what the buyer would base his claim on, in taking legal action.
IMO - I'm afraid the wording on your eBay auction has left you wide open to have legal action taken against you. You have mislead and lied on the auction.... although the buyer doesn't know you have admitted to 'guessing' what happened.