Many affiliate programs run with last-click attribution, where the affiliate receiving the last click before the sale gets 100% credit for the conversion. This is changing. With affiliate platforms providing new attribution models and reporting features, you are able to see a full-funnel, cross-channel view of how individual marketing tactics are working together. For example, you might see that a paid social campaign generated the first click, Affiliate X got click 2, and Affiliate Y got the last click. With this full picture, you can structure your affiliate commissions so that Affiliate X gets a percentage of the credit for the sale, even though they didn’t get the last click.
The phrase, "Affiliates are an extended sales force for your business", which is often used to explain affiliate marketing, is not completely accurate. The primary difference between the two is that affiliate marketers provide little if any influence on a possible prospect in the conversion process once that prospect is directed to the advertiser's website. The sales team of the advertiser, however, does have the control and influence up to the point where the prospect either a) signs the contract, or b) completes the purchase.
Affiliate marketing is commonly confused with referral marketing, as both forms of marketing use third parties to drive sales to the retailer. The two forms of marketing are differentiated, however, in how they drive sales, where affiliate marketing relies purely on financial motivations, while referral marketing relies more on trust and personal relationships.