Search for a DS Lite shell on any marketplace and you will find kits from a few euros to several times that. They look identical in photos. They are not identical on the bench.
The first difference is fit. A good kit clicks together with the same tension as original plastic: the seam lines meet, the hinge closes with a clean snap, and the shoulder buttons sit flush. Cheap shells warp at the screw posts, leave a visible gap at the front seam, and creak when you pick the console up.
The second difference is the finish. Original DS Lite plastic has a specific gloss depth. Good aftermarket kits get close; bad ones look wet or milky, and translucent versions turn cloudy instead of clear. Buttons are worse: a bad button set feels gritty in the well and rattles in transit.
The third difference is what you cannot see. Screw posts that strip on the second assembly. Light pipes that scatter the charge LED into the whole hinge. Lens adhesive that lifts at the corners after a warm day.
We have tested most of what the market sells, and the kits we build with are the ones that survived. It is a boring answer, but it is the whole craft: the difference between a restoration and a reshelling is fifty small decisions nobody sees.