My '89 is my baby. Sure, with any older vehicle, you'll run into issues... but if you're lucky, they're all fixable. Absolutely make sure you test drive it. Listen to the engine run... make sure there are no knocks or funky sounds. Make sure the shift knob doesn't wiggle while you're in gear (if it's stick shift). Crawl under it and look for leaks and cob-jobs of any sort. Examine everything under the hood really closely... make sure you don't hear any funny noises or encounter any funky smells. When I bought my YJ, I noticed a slight oil smell, but I didn't realize it was anything serious. Now I burn oil like mad. Pretty sure it's just a bad valve cover gasket, but who knows.
Anyway, just like buying any vehicle from a private party, examine it closely.
What engine's in it? Mileage?