In some cases, the purchaser arrives at a page where the affiliate cookie gets set, then leaves and makes a purchase via the PPC channel sometime before the affiliate cookie expires. Other times, the purchaser may click a PPC link, fail to make a purchase, but later purchase via an affiliate link. In both scenarios, the affiliate marketing channel played a part in the sale, but the role was different.
Cost per action/sale methods require that referred visitors do more than visit the advertiser's website before the affiliate receives a commission. The advertiser must convert that visitor first. It is in the best interest of the affiliate to send the most closely targeted traffic to the advertiser as possible to increase the chance of a conversion. The risk and loss are shared between the affiliate and the advertiser.
On one hand, long and ugly affiliate tracking links are a straight giveaway to people that you want to sell them a product (and people may be uncomfortable clicking on them). Therefore, making your link shorter and "nicer" looking will it give a more professional appearance. One of my favorite plugins for making links look "pretty" is the Pretty Links WordPress plugin.
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.