If the car is what he says it is then 4k is probably a pretty good price. If that is his actual asking price then 3500 cash should get it. If your worried about a twisted frame I can tell you some points to check. Go under the car, where you put a jack, and check the pinch weld piece that the rocker panel is connected to. Your looking for clamp marks from where it would have been on a frame rack. Check the front and rear impact absorbers behind both bumpers and make sure they're not damaged. Then check the strut towers and radiator core support for damage by looking for bends or cracked paint. Cracked paint could be a sign that there is damage. I also like to tell the guy to leave the car cold for me when I get there. I'll check all the fluids and even pull the oil filter to look for metal flakes. That let's you know the condition of the motor. Some people say its excessive but I dont care. Then if all that checks out you can start it. With the engine cold you can hear engine noise better. All that's left is the test drive. Good luck man. Hope some of this helps...
You can't lose if you put God first!
1989 LX, 306 with TF top end kit, Anderson N-21 cam, TKO 600 trans with steel splatter shield,full Maximum Motorsports Mustang maximum Grip box, Detroit locker rear end with 31 spline Moser axles. Staggered wheels with Nitto 555 315/35/17 out back.