Check every joint (barrel, upper and lower body, bell) for cracks by inspecting closely under good light, particularly around the tone holes where wood stress concentrates. Press each key and check for smooth return and correct sealing using a light test against each closed pad, similar to a saxophone or flute check. Check that the cork on each joint tenon is intact and not so worn that joints wobble or feel loose when assembled, since a properly snug fit is necessary for the instrument to stay in tune with itself across the joints. Ask whether the instrument has a recent adjustment history, since even a structurally sound clarinet can play poorly if the mechanism has drifted out of proper regulation.