Torque Test Channel took a $500 batch of iridium plugs from NGK, Champion, and Denso bought from Rock Auto, Amazon, and eBay, and found that about one third were fakes.
https://www.thedrive.com/news/ridiculously-in-depth-spark-plug-test-shows-1-3-of-them-were-fakes
I never buy auto parts off Amazon or eBay but know plenty of those who do. Stick with reputable sellers (like Pelican), or genuine dealer parts - though I've heard counterfeit parts are finding their way into dealer parts shelves too.