I've seen empty boxes sell well at gun shows too. Many many people automatically discard boxes and packing material. Compulsive neatniks and collectors don't, and are often willing to pay good money for what others wouldn't want cluttering their limited storage space.
Having the box exactly matching your goodie, even to the serial number if applicable, would be ideal. But a box with the wrong serial or slightly off in other respects still is better than none. Remember, due to the unfortunate habits of some, boxes are always rarer than the objects that go in them! 😀