Why do the marks on the casing of my Frontier Max Filter looks like it has been used?

The marks you see on the casing are caused in packaging because the surface of the casing is soft and has a thin coat of grease allowing its removal from the production mold.  You will see that the marks can easily be made on the surface but can be rubbed off or buffed easily.  If you remove the casing and rub the surface with your thumbs the marks will disappear.