Does you 3DS hinge make a click sound when you open it to its locked position? If it does I bet the top screen wobbles. This is something I have seen across the entire DS family of consoles with very few not falling victim to it. When you open the hinge it is supposed to click into place but the reason it wobbles is because the two hinge joints when locked into place have a few millimeters of space between them, others (like mine) do not click when opened but as a result do not wobble.
This (imo of course) is because Nintendo has the manufacturing tolerances set too high, likely to keep costs down. This happens in every facet of manufacturing, when a machine makes parts they are not all identical to the original spec, they have small variations every so many made. Now a manufacturer has the right to decide what it will allow to pass as "normal" and what must be discarded during the assembly process. The higher your tolerances the lower your defect rate, but this also makes manufacturing more expensive because you have to throw away more parts. and Nintendo likely upped the tolerance level when the DS Lite plastic was cracking a few years back because the hinges were too tight.
There are a number of things I have come across while buying DS and 3DS that are just not up to the level of quality I expect from a Nintendo product. On the DSi it was the hinges, on the XL its the hinges and the gloss top which is famous for having fallout stuck in it. The 3DS seems to have a number of issues the screen scratching could likely be solved by buying a Hori top screen protector (since it seems to happen after purchase not out of the box) but the paint quality is questionable and can be splotchy or thin, the top of the system tends to vary in color hue and its reflective quality. For example my blue one looks as intended but I have seen other blue ones that the top had no gradient scale to it and looked like a light green chrome color. This is likely why people are complaining enough to have Amazon pull it.