Simply put, online merchants (anyone who is selling a product) pays a commission to affiliate websites for sending buyers to them. It is up to the online merchant to decide if they want to pay a commission per sale, per click, per 1000 impressions and so on. They can even pay a percentage of sales (CPS) or a fixed amount per sale (CPA). Online merchants can also buy ‘space’ on an affiliate website in the form of display banners and ads.