Affiliate marketing has grown quickly since its inception. The e-commerce website, viewed as a marketing toy in the early days of the Internet, became an integrated part of the overall business plan and in some cases grew to a bigger business than the existing offline business. According to one report, the total sales amount generated through affiliate networks in 2006 was £2.16 billion in the United Kingdom alone. The estimates were £1.35 billion in sales in 2005. MarketingSherpa's research team estimated that, in 2006, affiliates worldwide earned US$6.5 billion in bounty and commissions from a variety of sources in retail, personal finance, gaming and gambling, travel, telecom, education, publishing, and forms of lead generation other than contextual advertising programs.
There’s a good reason why ClickBank is still a strong contender, however it does tend to focus more on digital products which may be of questionable quality. Yes, the review process is more professional these days, but it’s still primarily focused on selling digital products, especially “how to make money” courses and the like. That being said, there are some genuinely high-quality products on offer, and few affiliate programs are bigger than ClickBank, especially in selling (primarily digital) books.
The terms of an affiliate marketing program are set by the company wanting to advertise. Early on, companies were largely paying cost per click (traffic) or cost per mile (impressions) on banner advertisements. As the technology evolved, the focus turned to commissions on actual sales or qualified leads. The early affiliate marketing programs were vulnerable to fraud because clicks could be generated by software, as could impressions.
Affiliate marketing overlaps with other Internet marketing methods to some degree, because affiliates often use regular advertising methods. Those methods include organic search engine optimization (SEO), paid search engine marketing (PPC – Pay Per Click), e-mail marketing, content marketing, and (in some sense) display advertising. On the other hand, affiliates sometimes use less orthodox techniques, such as publishing reviews of products or services offered by a partner.