This may sound trivial, but being caught in a sudden downpour with worn, cracked or dirty wiper blades will quickly illustrate the importance of this simple maintenance check. A brief inspection of the wiper blades while cleaning off the windows will do it. Replace the blades once a year. If blades are purchased a parts supply store, ask for advice on how to put them on. And don't forget to keep the windshield wiper fluid full.
Dirty windows are a safety hazard.
Veteran race car driver Lyn St. James wrote an excellent car care and more book that was first published in 1984 and reprinted in 1989, so it could be about the same age as the used car you're buying. St. James feels strongly about developing good car maintenance habits, such as keeping the car clean.