My experience is that Costco is cheaper and entirely adequate/sufficient quality products, but rarely/never "top shelf" products (assuming that's meant to mean "the best").

This makes sense, as Costco is trying to move a lot of units and you can move a lot more units into the market that's looking for "perfectly adequate" than the ones looking for "the best". Honda outsells Porsche, Ferrari, and Lamborghini combined and all that...

That was the intent though. How can I buy cheap Chinese mass-produced products (usually low on the quality scale) but still have some basic quality bar that the products are not fraudulent? That they wouldn't fail basic safety standards or cause a fire or contain highly toxic ingredients. If I cared about higher quality for a given purchase, I wouldn't be choosing Amazon Basics. But for plenty of products (garbage bags, whiteboard markers, shop towels, etc ...) I just want the cheapest thing thing that actually will do the bare the minimum job.