looks pretty good seems a tad high but maybe he will haggle to 5000 but i live in an expensive market for rust free cars i would have to drive it and hear it run obviously the door speakers are aftermarket and IMO need to be gone after market stereo is gone look at whats left and see if there was a bunch of garbage wiring or if it was done corectly. steering wheel looks like an afterthought so it was probably replaced at some point but a grant wheel will fix that.

 

Looks like fair interior, but the pieces that need replacing wont be all that easy to do, or cheap. Especially the dash lower and pad. The pad is over $400, and a cover to repair the pad is $100. The lower dash is probably going to be a used item, as I'm not sure of anyone carrying those. Seat covers are about $250, if you can install them yourself, and expect to pay $400-$500 a pair to have them redone if you can't do them.
The car looks pretty straight, but check those trunk drops, as if the trunk seal leaks, the car can rust in the drops from just washing, and occasional wet driving. Put your hand down in there and feel for any hidden repairs. Also look closely at the bottom corners of the windshield. It's tough to see, and you'll need to look at that area through the glass. But look for signs of rust there, as it often builds up water from the windshield, and sits in that area to rust through.
If it's as solid as the seller says, then I'd want to get it for under $5,000 cash. I doubt he'll get the $5700 for a non Z28, and an automatic car with some issues.