Amazon leans heavily on convenience to sell lots of stuff. If I have to read a handful of reviews and cross my fingers whenever getting a legitimate product is important, is it really so convenient? So far the market says yes, but I sure would move elsewhere if there was an elsewhere.
The OP suggests bn.com (Barnes and Noble) for books. I haven't tried them myself. Yet.
For household goods I like walmart.com (the sold-by-Walmart items, not the ones from 3rd-party sellers). Free 2-day shipping (in the US) for orders over $35. A supply chain that (I hope and assume) does not allow 3rd party sellers to introduce counterfeits, unlike the so-called "sold by Amazon" items that are promiscuously commingled with items supplied by 3rd-party sellers.
So for anything where a counterfeit product could pose a health risk, I check walmart.com first.
(I feel a bit strange touting Walmart as the underdog, since it certainly comes with its own set of baggage, but it does seem to be one of the few companies big enough to keep Amazon from gaining a complete monopoly).