Look for rust. It's there, you just have to find it. Start UNDER the car. It isn't worth fixing rust on a 123, so decide if it's bad enough. The floor pans rust, the firewall (by your feet and your knees) rusts, the frame rails rust.
Give a mechanic you trust 20$ to check out the suspension, brakes, emissions, tires, exhaust.
If it will pass inspection, then you have a wonderful car. If it doesn't pass inspection, then don't even think of buying it.
Parts are redily available (and inexpensively if you DON'T go to the dealer), as is good service info if you want to DIY.