Reddit:

Since I started noticing this issue, I’ve gotten counterfeit batteries, counterfeit shampoo, and counterfeit guitar strings, and they were all sold by Amazon.com. It got so bad that I completely stopped using Amazon.

The bigger question is “what the hell is going on?” This didn’t seem to be a problem, say, 5 years ago. I started looking into why this was the case, and I found a pretty clear answer: commingled inventory.

And:

Let’s say I am a third-party seller on Amazon, and I am selling Crest Toothpaste. I send 100 tubes of Crest Toothpaste to Amazon for Amazon fulfillment, and then 100 tubes are listed by me on Amazon. The problem is that my tubes of Crest aren’t entered into the system as “SolitaryEgg’s Storefront Crest Toothpaste,” they are just entered as “Crest Toothpaste” and thrown into a bin with all the other crest toothpaste. Even the main “sold by Amazon.com” stock.

This is a fascinating read. In a nutshell, the logic here is, commingled inventory means a counterfeiter can dump their bad goods into the river of genuine goods and never get caught, since the goods are not validated until the end user receives them.

Not sure this is fixable, since the cost of validating goods on the Amazon side would be enormous, a non-starter. One thing Amazon could do is prevent third party goods from entering the validated goods stream. That way, when you make a purchase, you could choose “validated” goods or “take a chance” goods.