Affiliates like ereaderiq could just not put their tags on free ebooks, I suppose. I rarely pick up free ebooks based on their links, just books on my watchlist that have price drops.
I have a question. If I click on an affiliate link for affiliate A, don't buy anything, and an hour later, click an affiliate link for affiliate B, does that overwrite the cookie? I would wager that I click on a lot of affiliate links daily.