How could you tell that they were counterfeits?
Its all over it, just look. "100% compatible with the originals." if nothing else.
Do you see original logos? Do you see it mentioned over and over how its original or OEM? You shouldn't be looking for reasons why its not a good buy, on such places you should expect it as default and try to give reasons why it actually may be an OK buy.
I simply wouldn't be buying such things from Amazon to start with, since seller can easily put those words there for quick profit, stickers can be fake and that's about the remote analysis that can be done, reviews are often gamed and useless. Its aliexpress/temu equivalent, nothing more.
The jeans I liked so I went and bought some at an actual Lucky Brand store. Not sure if you've ever felt Lucky Jeans but they're super soft. Mine were not the same denim or cotton they used. Mine felt rough, not as good quality.
Same thing with the keyboard. I ordered one off of the MS site. Got it and started using it for my work keyboard and immediately grabbed the other one I was using for my personal work. Subtle differences, but the one I got on Amazon was not the same. Rubber on the mouse was different the keys felt different, they had a different sound than the real one.
The JBL speaker my son pointed out the inconsistency in the logo letters. Got his real JBL cans and showed me - it was close to the naked eye, but when you saw it against the legit logo it was obvious.
The shorts and work out gear had that Chinese factory smell when it came. If you've ever bought stuff directly from China, you know what I'm talking about. Again, pulled out some of my other stuff I had bought that I knew was real and same thing, logo inconsistencies, poor stitching in areas, different thread than the originals.
Again, I ended up catching all these well after the fact, but the fact remains that stuff I thought I was buying on Amazon, was not. The troubling thing is it happened across products I would never suspect would be counterfeited.