Consumable goods, eg. Toothpaste are things that you may want to be genuine. Sure it may say "Crest", but did it come from the Crest factory, or did a no-name company drop ship fake crest toothpaste to an amazon warehouse, and now their product is co-mingled with genuine crest?

(this is an example, you can google for real stories)

To add, there are stores of extreme coupons who will products (again, lets use toothpaste) from brick and mortar stores on discount, then sell them on amazon. Or buying returns/expired food products from brick and mortar stores, then selling into amazon.

Again, the issue in all this is co-mingling because any genuine sourced products compete with these less reputable ones.

We are not talking here about laptops or cameras. The usual targets for counterfeiting are things like USB cables or headphones.

They might come without packaging, but then so do the geniune ones sometimes. They look normal to non-expert eye, but then when you use them they either break quickly, or whilst functiontal are not as effective as a genuine item(worse sound quality, slower charging, slower transfer speed etc.).

Okay I didn't realize that was implied with the context. So you can't use Amazon for buying genuine USB cables, headphones, or toothpaste. But laptops, cameras and phones are okay.