There’s a big difference between limiting SKU count to simplify operations and products being curated to be “the best” and most trustworthy options.
Natural foods stores have much more stringent standards on things like artificial colors, animal treatment, and use of chemicals.
For example, Tide Original is banned in New York for having too much of a cancer-causing chemical. Costco sells it. Costco sells products with artificial colors linked to ADHD in children. Costco’s best organic eggs are visibly and nutritionally inferior to eggs from pasture-raised chickens.
The fact that Costco doesn’t sell low quality private label and discount brand items has more to do with customer demographic than trust and curation.
This is also the store that allows third-party companies’ representatives to harass customers about solar panels and DirecTV in the store. “Trustworthy.”
They’re really no different on “trust” than Walmart or Target, and I think people need to stop being a part of its retail cult and take it for what it is: a store with good prices on staple goods.
No one said Costco offers the very best product in any or all categories.
What they said is that Costco is upfront about what they're selling, rarely sells defective products, and offers a very generous return policy in the (rare) case you are dissatisfied with a purchase.
Those aren't that far off from Walmart or Target, because those are also generally reasonable retailers. I would say Costco offers better value on their products overall.
If you ask more of that from any retailer, good luck finding anyplace to purchase anything.
I don't know if we can say that a store with unlabeled aisles can be a source of curation.