I always wonder why people wouldn't fix it before selling.
Going on my own experiences (that's the only thing that's important isn't it?) I think it's because a lot of private sellers think they will lose loads of money if they pay a big wad, sorting out their pride and joy, only to get offered the same amount, or hardly any more, than if they did nothing to it at all.
In some ways I agree with this strategy...
My experience with all the cars I have sold privately, has been of p***takers not wanting to pay a penny extra for a lot of money I spent getting these cars up to immaculate condition (new tyres and tracking, paintwork detailing, new tax disk, etc..)
I now play hard-ball when I sell privately and don't give an inch.
This is just my experience when selling privately and I think we should get away from the notion of it being the seller's duty to take a hit when selling a car and spending a lot. We can debate this forever, just my 2p worth of course.