To answer some of these questions:
1. Texture isn't going to match it is 3d printed
2. The edge lines up with the edge that is already there (see picture 1 in post 1). It can be made to go along the cup holder but that will complicate it more and give pointed edges where things can get snagged on which is not good. Also there is no place to secure the piece down there other than if you double sided tape it.
3. I can bevel the edge, i will see how it looks, but yes i am sure a power plug will fit because i use mine
-Thank you very much for the comments and suggestions (sincerely) they are good feeback and help me develop this piece.
Also a few posts up it was asked how thick the piece is. It is 2mm thick and is slightly raised over the stock slot. I can do 1mm to make it more flush, but that might make it too weak. If you plan on putting it in and not removing it a bunch of times 1mm might be fine though.
I'm not sure if you've seen my OBDelholster, which I've sold on this forum, but it is also a 3D printed piece, which I sand and paint before shipping. I offered it as a plain printed part, or finished. Only one out of almost 50 orders were for the finished part. It's a lot of work.
I'll echo some of the comments by others-- I agree with the idea of just printing the part and shipping as is, letting the buyer sand and paint as he wishes. Having a rounded edge around the 12V socket bore would be nice. Depending on the thickness of the cover, something like a 5mm radius could be nice. On the other hand, if the cover is sanded extensively, this can alter the appearance of, and even eliminated, the rounded edge. The buyer can also just sand a soft edge into it if desired.
What plastic are you using? ABS? ASA?