I have this experience probably about half the time I'm shopping on Amazon (which I do a lot of). If you look in the comments/reviews for many items there will be dozens of people saying e.g. "product shipped was not the product pictured", "only buy if the seller is so-and-so if you want a genuine product", "received a used/returned product", and on and on. I've taken to spending more and going out of my way to buy some things in retail stores, where I can at least be reasonably sure I'm not getting a counterfeit.