Can someone give me tips on how to negotiate on a car?

i have my eyes on 2 prius', they are just a couple grand out of my comfortable price range. I believe they are 07's and their asking price isn't ridiculous, but according to kbb, going down a grand or two is still a good asking price.

my father isn't much help, because he is set on a honda or some other toyota. How can i talk them down? I'll have to be doing it online, because i'm not exactly willing to make the drive by myself as i am 20 year old not very intimidating girl. But i would make the drive if i really needed to go.

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