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.
In the case of cost per mille/click, the publisher is not concerned about whether a visitor is a member of the audience that the advertiser tries to attract and is able to convert because at this point the publisher has already earned his commission. This leaves the greater, and, in case of cost per mille, the full risk and loss (if the visitor cannot be converted) to the advertiser.