Best advice I can give you from having sold cars.
Wait till the very last day of the month and late at night. Like 930. Then go in with specifics you want and know the market value of the car. During this time period, most all car lots will do what they can possible for a sale to bump their number for the month.
If you can also find the buyer for the lot, they sometimes do business on the side and will look for a car for you at the auctions and possibley look for one for you. Usually the car lot will take a cut for their "pac"(anywhere from 250-500 usually). So if you can manage that, you can get a really good deal.
<>Bryan<>