The Wirecutter is the best example of an affiliate site that I've ever seen. I wouldn't even put it in the same category as what you'd think of as an affiliate site, aside from how they make their money. Brian Lam's a great example of someone who sticks to a principle and then grinds it out to the nth degree. Can't say how many times I've used that site (and TheSweethome) for product reviews.
The seller, whether a solo entrepreneur or large enterprise, is a vendor, merchant, product creator, or retailer with a product to market. The product can be a physical object, like household goods, or a service, like makeup tutorials. Also known as the brand, the seller does not need to be actively involved in the marketing, but they may also be the advertiser and profit from the revenue sharing associated with affiliate marketing.