For a quick used-lens check, first know the normal behavior of that specific lens so you can tell expected flaws from a bad copy. In a short, uncontrolled test, do a general inspection and then make a few sample images you can review closely on the camera or, better, on a laptop.

For wide-angle lenses, pay special attention to:

• center and corner sharpness
• chromatic aberration/fringing
• vignetting
• distortion

Shoot the same kind of scene at a few apertures: wide open, around f/8, and stopped down further (for example around f/22). Check both the center and the edges/corners. Look for unusually soft corners, excessive fringing, or image quality that seems much worse than reviews of that lens suggest.

Because wide-angle lenses naturally show some distortion, vignetting, and edge softness, the key is whether the results are in line with the lens’s known quirks. If possible, ask the seller for sample photos taken with the actual lens beforehand. If you can’t evaluate files carefully on site, buying from a reputable dealer with a return policy is safer than relying on a brief in-person test alone.