It all depends what you are buying, if its a rare car then the seller has the advantage, if its a commodore then the buyer has the advantage because there are always heaps on the market to choose from. Many people will price a car based on what they think its worth, not what the market says its worth.
A person might buy a car for $4000 and then put $3000 in bits an pieces into it to make it nice, that doesnt make the car worth $7000 but some people think it does. They might get lucky and find a buyer who wants exactly what they have on the car but for most people there might be things that they dont like so arent prepared to pay for.
I always do heaps of research find out what a high km model is worth and then what a low km model is worth and then i can have a gauge of price range for vaying km's, then you factor in the condition. Is the paint peeling, is it faded, are there heaps of carpark dents and scrapes that will need touching up etc. Most people will take these issues into account and price accordingly, like buying a hail damaged car. Some people dont, so tell them whats wrong and haggle accordingly. People always add a few hundred onto the price and all people will have a minimum price that they want to achieve in their mind. Your job as a buyer is to offer a little bit lower than this price and then have them come back with a counter offer, if they accept your offer first up well thats a bonus. And then as Junny said have the cash with you, people loose their sense of value when they see a wad of $50's and the thought of getting all those 50's in their hand now makes some people accept stupidly low offers. Matt