over packing items---overkill?

Sometimes it may be what is at hand?
If folks reuse packaging, then it may have been the box they just happened to pick up. Especially if the company is using younger adults to do the packing.
(less concern of a waste of packing materials)

I have an example of this from when I purchased a McCormack DNA-1 Deluxe from Goodwin's High-End. They used a wooden box with heavy padding on the inside. This box/crate was used for a more expensive amp but rather than have to look for another box and padding and throw out the wooden box they put the DNA-1 Deluxe in there and sent it to me. The wooden box had metal handles on each side for 2 people to carry the original amp. I was shocked when I got the DNA-1 Deluxe and saw all the packaging.

Now whenever I package stuff I sell here I try to go the extra mile because one can't be too careful with couriers. Also I've heard the horror stories of buyers shafting sellers on transactions due to packaging.

I had a Rogue amp that was obviously dropped during shipment and the cover was dented and sheared off all the top screws in the process.

as far as I am concerned, overpack away!!!

And if it wasn't packed well and another item or sharp object punctured the package in transit and ruined the first five or so sleeves then what would you post.
Cheers

No such thing as over packing.