Diagnosis
The matte-finish plastic casing is prone to scuff marks and plasticizer transfer from bags or other plastics resting against it.
How to Fix It
Use a microfiber cloth dampened with a mild solution of dish soap and warm water. Wipe gently in one direction. For persistent marks, apply a small amount of isopropyl alcohol (70%) to the cloth, not directly to the unit. Test in an inconspicuous area first.
If That Didn't Work
Avoid abrasive cleaners or magic erasers, as they will permanently dull the finish. For ingrained grime, a specialized plastic cleaner like Meguiar's PlastX, applied with a soft cloth, can restore the surface.
Heads Up
Do not use window cleaners, all-purpose sprays with ammonia, or solvents like acetone. These can cause permanent clouding or cracking of the ABS plastic. Always unplug the unit before cleaning.