Make sure you get the title document.
Make sure the car rolls, and does not come on 4 flat tyres, or with siezed brakes.
Make sure everything is there, no missing gearbox, steering wheel, engine, seats or spare wheel.
Expect to have to renew the wiring loom, everything rubber, expect holes in the tops of the fuel tanks, expect the exhaust system to be stuffed, the seats to be siezed in their runners, and the door hinges to need replacingand probably the brake and accelerator pedals to be rusted solid.
Try to make sure the engine turns and is not siezed.
The windscreen will leak and the wooden dashboard will be falling apart.