Use variety. Mix and match affiliate ads so you don't overwhelm your visitors (content-embedded affiliate links usually have the best click-through rates over image links.) Consider using a lead page and funnel system to market your affiliate business. Lure prospects to your email list with a free offer and include links to your affiliate product pages.
Spam is the biggest threat to organic search engines, whose goal is to provide quality search results for keywords or phrases entered by their users. Google's PageRank algorithm update ("BigDaddy") in February 2006—the final stage of Google's major update ("Jagger") that began in mid-summer 2005—specifically targeted spamdexing with great success. This update thus enabled Google to remove a large amount of mostly computer-generated duplicate content from its index.