That looks like a fairly average S30 that you'd find in the Southwest US or California. The stock frame rails have definitely been covered with an aftermarket repair rail not unlike the BadDog rails. The floor has been patched on the left side as noted above. The undercarriage could use some attention but that's pretty common - make the top look good, people rarely look underneath. I've seen a lot worse even here in Arizona where we have almost no water...
Those pics aren't going to tell you the whole story. You're going to want to look under the hatch at the sill corners, the door bottoms, the rockers, the dog leg in front of the rear wheels, the bottoms of the front fenders, under the cowl, under the carpet and seats in the cockpit and maybe the spare tire well. On a 280Z you might want to check around the windshield frame as well. Look for bulging of the paint in any of these areas.