Great question — answering as the UphillTech team:
There are many components within the Joomla extension libaary which should be able to help, here is a couple as an example: WizAffiliates VM Affiliate - Requires Virtuemark For even more check out Joomla extensions library for Affiliates If you can't find something suitable then sadly your need to make your own or have someone do it for you.
Full answer by Simon Hayter: https://webmasters.stackexchange.com/a/43755 (CC BY-SA 3.0).
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