The June 2012 leaked version of the Google rater handbook(I dont know if there is a newer version) tells human evaluators to consider pages differently depending on intent. Action, informational and navigational. I see affiliates trying to target action visitors with informational pages and this just doesn't work right now. Action pages for shopping require a checkout cart, help options and preferably an address and phone number. Comparison, reviews and other buying features also help. These are things affiliate sites often lack.