What would have happened if he'd turned up and offered you asking price @Spygoat ? Presume you'd have let it go?
I know it would make sense to sell this (and many other parts) separately but I have gone down this road before, stripped all the parts and sold them then changed my mind on selling the bike! If I sell it as it stands I cant change my mind half way through. Looks like it will be with me till next year anyways so probably change my mind again lol.
There is some interesting legal point to that as well - something about offering something for sale - someone makes an offer (a bid) - you refuse - there is no obligation for you to have to go back to the original price and accepting that.
Absolutely, you are never obliged to sell no matter how far they travel or how much they offer. However if someone had travelled to see my bike and they offered asking price then they'd be leaving with it. To let them travel and offer full price then change your mind just isn't cricket. I'd have no problem ringing someone the night before and saying I'd changed my mind though.