A general FYI: some insurance companies do offer fixed-value policies, with a pre-set payout for total loss.
But those policies come at a premium. And the DC Integra is outrageously expensive to insure as-is.

If the cost of insurance and risk of theft don't faze you, by all means go for the well-maintained single-owner car.
I'd offer $6000 and see if he takes it.

Yes, the craigslist cars are dime a dozen, but most have been ridden hard and put away wet.
That kind of bargain is no bargain at all.