Education occurs most often in "real life" by becoming involved and learning the details as time progresses. Although there are several books on the topic, some so-called "how-to" or "silver bullet" books instruct readers to manipulate holes in the Google algorithm, which can quickly become out of date, or suggest strategies no longer endorsed or permitted by advertisers.
I concluded that having read a product review, people felt more informed to make a purchasing decision. As a result, if they did click a link after reading the review they were more likely to buy the product. Those clicking on the top link seemed to be more in a ‘surfing’ mode. They clicked on the link less because they wanted to buy it but more out of interest to learn more. Some bought the product and some bought other products once they were ‘in the door’ at Amazon.