> Yet throwaway brands peddling junk that wouldn't have realistically made it onto the shelves of a big box store is a real problem on Amazon's marketplace, and other similar ones.

Either it's a defective batch of products that would have been sold under a brand name or its junk that would have never been sold at all. Both of these can't be true of the same product.

I'd also argue that being sold at a big box store is not really indicative of much in the 21st century.

If you haven't already, I'd recommend spending some time reading about what it takes to get a product on the shelf at Wal-Mart/Target/Costco. When a companies reputation relies on what it is selling, the bar becomes a lot higher.