That doesn’t tell me anything when Amazon provided no guarantee that the item I’m ordering is from that vendor. I’ve been burned many times with cheap fakes. It’s clear Amazon does nothing to ensure I’m getting the original product. As long as the upc matches, they’ll ship it.
Magic the Gathering cards come to mind! Buying MTG cards from Amazon can be a little risky as there is a non zero chance of getting a box with already opened packs [0]. Customers buy the product, take the valuable cards out, reseal it and return to Amazon. Amazon just throws it in with the rest as they doesn't know how to properly check for tampering.
This has nothing to do with Amazon or co-mingled inventory, and everything to do with shitty customers. Non-Amazon sellers would have the exact same issue. At least with Amazon, I have regress as a customer and know that things will be made right regardless of the circumstances of the sale.
There's plenty of ammo to use if you want to take potshots at Amazon, but this isn't one of them.
I wanted to buy a Sony phone direct from Amazon. I specifically bought "Shipped and Sold by Amazon" three times and had to return it three times because they kept sending me another seller's commingled inventory. It was obvious because the box had the third party seller's sticker on it and it was a Hong Kong model phone which would not work properly in the USA.