> I see these complaints often enough that I assume people aren't just lying outright, but I personally have never had any of this happen to me despite all of the junk I've bought on Amazon.

I think this is a symptom of co-mingling inventories. You can 'buy it from Amazon' or buy it from 'Joe's super legit online shop' for $0.30 less. I suspect many reviews of wrong or broken products are coming from some kind of drop-shipping operation and the buyers aren't aware they're buying from a 3rd party seller.