While I agree with about 98% of your post, I don't with a couple points.
While I agree with your using Post Office boxes, they don't have anything that fits a lot of what I sell, and flat rate can be more expensive than parcel post. Not a good way to keep those shipping costs down.
I also disagree with using only new boxes. As long as the ones you use are clean and not all banged up, people aren't going to judge you on which box you used. And if they are, nothing you can do will make them happy. Use a recycled box, but make sure it's clean and that you pack your item well.
And last (I guess it's 3), most people aren't going to give you 5 stars because you give them a pen. They want what they ordered, in the condition that it was listed in. Will I buy something of yours again because you gave me a pen? Nope. Only reason to reorder from someone is because they have something I want, at a price I like, who sent my item promptly, and was shipped to arrive in the condition it was advertised.