Well the easiest solution is to go back to having Amazon be the seller of products on Amazon, but we all one that ship sailed.

But if the problem is shared bin storage, the solution isn’t free, but it’s also not as expensive as lots of buyer confidence:

Tag every item with a QR code indicating its source when it comes into the distribution center. Use that code to identify the bad actors when there are returns and ban them.

“But what about products not shipped by Amazon?”

In that case, you know who sold and shipped the product, and if they can’t get their shit together they shouldn’t be allowed to work with Amazon.