The problem is that if you don't know to pay attention to the seller, you can end up buying from a third party while looking at a first party product page.

That is a misleading statement because Amazon only commingles third party sellers, not their own inventory. If you buy from "Amazon itself" you aren't at risk of getting commingled inventory.

"The system has enabled Amazon to make better use of its warehouse space and keep a wide variety of items in stock around the country. The idea is to give Amazon flexibility to ship certain products based on their proximity to customers, speeding delivery times. For third-party sellers, it saves them the trouble of having to label individual items sent to the Amazon warehouse. The bar code takes care of that. But the practice has in some cases led to mix-ups between counterfeit and authentic products, even when they are sent by Amazon itself."

That would appear to be why Wusthof knives, for instance, forbids any authorized retailer from commingling and doesn't count Amazon as an authorized retailer.