Affiliates were among the earliest adopters of pay per click advertising when the first pay-per-click search engines emerged during the end of the 1990s. Later in 2000 Google launched its pay per click service, Google AdWords, which is responsible for the widespread use and acceptance of pay per click as an advertising channel. An increasing number of merchants engaged in pay per click advertising, either directly or via a search marketing agency, and realized that this space was already occupied by their affiliates. Although this situation alone created advertising channel conflicts and debates between advertisers and affiliates, the largest issue concerned affiliates bidding on advertisers names, brands, and trademarks. Several advertisers began to adjust their affiliate program terms to prohibit their affiliates from bidding on those type of keywords. Some advertisers, however, did and still do embrace this behavior, going so far as to allow, or even encourage, affiliates to bid on any term, including the advertiser's trademarks.
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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.