Be careful of anyone who list a car with a reserve but in the body of the description offers a very low buy it now price.  (Not Ebay's buy it now)  Usually after you email them, they'll ask you to call them etc.  What they want is for you to send a wire deposit to them to stop the listing, and once they do they'll disappear.  

Also,  Always, always use ebay email for asking questions especially about the cars condition, add on cost etc, etc.  Otherwise, if disputed arises, you get into a he said she said scenario.  Stick to email for documentation & proof.  Call only when you have to.  To make contact after you won etc.

Obviously there is more to watch out for, but I seen this done more than a few times.  One more thing, be very careful of sellers that have just register with eaby, and have a fantastic deal.  It could be true, but check it out VERY CAREFULLY!!