A lot of wringing of hands here over a problem that just doesn't appear to be much of a problem. As others have pointed out, if stuff was getting damaged at a significant rate we'd see a change.
My experience is that Amazon, B&H and Adorama all occasionally pack much worse than the average private seller. But even so, not many issues. And if there is an issue they cover you without much trouble.
The one thing worth exploring is insurance taken on private sales. I see people saying they insure used items at full replacement value. I think that is a waste of money. From what I have been told, you may be able to recoup what you sold it for, but you'll need proof of that sale, with an address that matches the ship to address. I was told that an eBay transaction was pretty solid in terms of proof, but more private sales become questionable.
And, if it is a matter of damage, not a lost package, you are likely to get push back about packaging. Bottom line is that you should not assume that insurance is a no-brainer. I use a shipping service when I am concerned about it. They pack it and at least own that part of the responsibility.