Rotate the focus and zoom rings. They should move smoothly without grinding or "zoom creep" (the lens extending on its own when pointed down).

Lenses with plastic mounts, like older kit zooms, are often very cheap. While they may wear out faster, they are capable of sharp images in good light. Community Insights on Used Gear

Shine a flashlight through the lens. Look for fungus (looks like spiderwebs or crystals), heavy dust, or a "cloudy" haze. Small dust specks are normal and rarely affect images.

Old manual lenses from the 70s and 80s (like Nikon AI-S Go to product viewer dialog for this item.