You could either use tracking URL`s (plenty of scripts available that let you use unique coded type URL`s so they can be set-up for different traffic types) and this is then captured in the refers of the respective sponsor (can vary depending on the affiliate software that the sponsor is using).
Another method (but a little excessive) is setting-up duplicate pages which you would target to the particular traffic you are buying. Also, some of the search engines allow you to set-up unique URL`s so you can accurately track the success (or not) of the clicked delivery.
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