The summary is that you need to offer something so low that it would be a screaming deal for you, but just high enough that the counterparty thinks you're serious.

Then, you work from there (avoiding tactics like "splitting the difference/meeting in the middle" that might pull you up much higher than you need to go, much more quickly than you need to go).

Of course, it's tough—car salesmen literally do this all day, and there's an information asymmetry in that they know how much they need in order to break even and you don't.

Your best leverage is your ability to walk away, so keep that in mind and don't fall in love with any one particular car; especially (1) a Kia and (2) a salvage title vehicle... I say this with all the kindness in the world, but missing out on this vehicle might end up being the best outcome for you.