it has been estimated that Amazon gets upwards of 40% of its sales from affiliates or “Associates” and third party sellers who list and sell products on the Amazon website(s).
An Associate is an independent seller or business that receives a commission for referring customers to the Amazon.com site. Associates do this by placing links on their websites to the Amazon homepage or to specific products. If a referral results in a sale, the Associate receives a commission from Amazon.
It is fairly easy to become an amazon associat, you apply and are usually approved within a few days.