take a small hammer and screwdriver.
crawl under the jeep and look at the frame,
no matter how well it runs and looks on the outside, if the frame is rusted up or rotten you have a serious problem.
jeeps are bad for electrical problems, check all switches and lights, if the motor is warm when you get there seller may be covering a hard starter when cold.
ask that the motor be cold when you come to look, otherwise you are sunk, as you might have to wait until the next day for the motor to cool off.
some old jeeps will not start well the next day, they have fuel related problems.
be sure all the shrouds are around the fan, otherwise the motor will get hot, must have proper air flow.
just a few things to think about. how does it drive on a rough, bumpy road, most old jeeps are worn out in the front end, and it will cost more than the jeep is worth to fix or repair the front end.
many that have a old jeep for sale have been waiting for pretty sunny days, so they can set the old jeep out on the road for sale,
hoping potential buyer will only be thinking of how cool he is going to look driving a jeep with the top down, not thinking about all the mechanical, electrical and body problems of owning an old jeep.
good luck with your purchase, all take another old school jeep owner with you to look at the jeep.
he will know more what to look for.