Check the frame, look for dark spots around the engine or dirty spots, dirt tends to cling to leaky areas. start her up, listen for ticks in exhaust and the head. If there's no rust and she sounds fine, I wouldn't have an issue w purchasing the jeep. They are very easy to work on and diagnosing issues is a breeze on a 98.
If there is an exhaust tick, have them fix it, then purchase.