I've never sold a car on ebay so I can't give you a definite answer but I would imagine it may depend on exactly what sort of car you are selling.
I think most customers would want to come and see the car for themselves and maybe get it road tested. I know I would, at any rate.
So from that point of view, you may be better with a classified ad as you could allow this.
If I have my facts right, I don't think you can exchange addresses etc with potential customers before a sale in the 'Buy it now' category.
I could be wrong, I guess check out the ebay terms and conditions for car ads.
I suspect though for most types of car sales, people will want to come see it and negotiate a little bit on price. That may be different for vintage cars or collector's type cars.
