Yep.  I actually pull up the highest priced current item I can find as comparison to proof of value, and I've never had an issue.   (Although all of my claims have been under $50, so maybe they just rubber stamp those)
 

Sure, I'll deliver this package, but if I lose it, it's not my fault! For an extra 2 bucks I'll take responsibility for doing the thing you already paid me to do.

Exactly! Nailed it!

Usually Priority is only a very small amount more than First Class, and I think it comes with $50 insurance, and you can buy more for something like $1.50 per $100. If it's an expensive item, you may just want to do it. Of course it's a waste of money most of the time, but that one time it will be worth it (and you will have forgotten).

The entire system is broken. Sellers have nothing to do with how the package is handled in actuality.

Yep, had one happen to me. Luckily had an extra game so I just sent the buyer another one and it solved that issue. It is a shame that USPS seems to get away with everything. Just one of those uneasy dealings with selling online.