Affiliate deduplication is a particular form of conversion deduplication applied to affiliates.
Most merchants use several affiliate networks to promote and develop their affiliate programs. If a buyer has previously clicked two affiliate links on two affiliate websites wich belongs to two distinct networks, the merchant who is not using deduplication has to paid two commissions for a single order.
Experts estimate that for large affiliate programs, no deduplication could lead to more than 20 percent of wasted affiliate budget.
For preventing the phenomenon, merchants deduplicate conversion between different networks. The most common practice is to attribute the sale and pay the commission to the last cookie, but the practice not always awards the best contributor to the sale.
More complex deduplication methods can be used and based upon:
the number of time an affiliate is involved
the relation between the ad or link clicked and the purchased product
the duration and content of the visit
Affiliate deduplication can also refers to deduplication against other marketing channels. See conversion deduplication and attribution model for more details.
Affiliate deduplication is often made by the way of conditional tagging by which only one affiliate network conversion tag is fired on the confirmation page. It prevents the affiliate to see commission cancellations as it is with a later manual control of commissions.
It has to be noticed that, even if a merchant has a good knowledge of each channel real contribution by the way of a complex attribution model, it is very difficult from a practical point of view to share commissions between contributor channels.
Merchants are not always very transparent about their affiliate deduplication.
Examples of deduplication policies:
Image credit Wiki Affiliate Window