I think the best time to buy a car is at the end of December. From anyone.
This pretty much, but also be prepared to just walk away if the Dealer is playing hardball. Yes hell probably sell the car anyway, but at some points in the year hell be more inclined to give you discount. I picked up my old Mk2 Astra SRi for cheap because the guy came wandering out of the compound as I was about to drive off. Always be less willing to buy than they are to sell. Over the years Ive usually pulled back about 15% off the screen price of the cars Ive bought. Ive rarely gone over £2000 in actual payment, but Ive had cars with screen prices over that. Buy at Christmas, and the end of Feb as the Christmas Credit Card bills come in!
That didnt work this year. Although cars were cheaper at xmas (like they should be), the price of used cars has rocketed since due to the scrappage scheme.
Time will tell this year, but the prices have been firmly high since, i dont see any dropping off as yet.