There is a joke(s) that you must sell a lot online because:
(I forget most of them, but on eBay community pages for sellers forum there was a long running list of these jokes)
But heres a few I do remember, <You are driving down the street and see a box on the side of the road and stop and pick it up because its a perfect size for shipping, You are on a first name basis with at least 3 people at the local post office, as well as your UPS route driver, You share recipes with these same people. And my own contribution was, when I ran my shop at our old farm, the UPS driver rerouted his daily route so he stopped during lunch time because sometimes my wife would feed him or give him samples, Also when we moved, For years my wifes family had given me grief about long hair, After many years I cut it short, but no one noticed or said anything. The first person who did was our UPS Driver,, "Dude! Did you cut your hair?" My wife almost fell over laughing so hard.
So, yes, You ARE correct. USPS is bad, but in many cases I would say UPS is just as bad, They also hire a lot of seasonals and package sorting and loading/off loading at airport terminals is an entry level job, so stuff gets abused. I use some creative solutions. I have NOT been doing much sales online for the last 5 years, but I used to and now downsizing so will be a lot soon. I have in storage many trash bags packed with styrofoam peanuts, and in my shed is a range of boxs, I buy tape by the case, And my wife yells at me for how much tape I use. (You can never be too sure or safe is my moto)
So, I would rather use a larger box and some extra weight than I would have a claim, especially for an overseas buyer.
I also have an unlimited supply of sheet styrofoam (used to be recyclable, but the one resource went away)
Air bags and bubble wrap, and Egg cartons, foam rubber sheets too. Here is one solution I learned from another guy who sells car parts on eBay. He cleans and washes plastic milk jugs, shampoo bottles, salad dressing etc etc. Lets say you are shipping a very heavy cast iron part. As you say, A box in a box is a good idea, then you line the gaps with a clean and sealed plastic container with the lid on securly. I researched this and found the burst strength is astronomical, yet the cushioning of a air filled plastic container is way higher than styrofoam. I have used that method when I used to sell on ebay a lot, and some people got it, but I got a couple complaints of "Why are you shipping me your garbage?" However nothing got broken and so I made up a explanation and printed them off and included it in those packages along with the suggestion to take the empty plastic containers and put out in their recycling. Nobody will take styrofoam peanuts except another shipper so the plastic containers is more enviro friendly.
( We have another recycling crisis as well on plastics, Apparently MOST of our regions plastic was sold to China, but for trade and other reasons they stopped buying it, now many places wont recycle it, However read an interesting article that the Netherlands uses plastics to make roads out of which seems a great solution)