The conventional wisdom here on HN is that every single item sold on Amazon is fake, without exception.

Realistically, there are probably some legit 18650s and lots of fake ones. But it could be difficult to figure out which ones are legit before buying them. Co-mingling of warehouse stock is often cited as a reason why this is impossible: a legitimate seller may list their items, and then some sellers of fakes come along and state that they are selling the same SKU, and Amazon will mix all of these in a single bin in the warehouses, and you don't know which one you're getting in your order.

Probably not many real cells on Amazon, I looked quickly and the first 2 pages didn't have a single legitimate cell, but there are several online stores that sell legitimate cells like 18650batterystore.com