The last time I saw an Amazon employee weigh in, he said the ads are in fact not effective but the ad team isn't measuring it well. In particular, he claimed that he showed them that after adjusting for returns, the order-again rate for a particular expensive item was effectively zero, they asked him to repeat his study for another product, and he wandered off and found work to do for his own team.
My skepticism level remains high. This is billions of dollars, with easy access to tons of data.
I'm not sure if put more stock in the government successfully hiding a fake moon landing, or analysts in one of history's most successful companies not running the numbers.
The last time I saw an Amazon employee weigh in, he said the ads are in fact not effective but the ad team isn't measuring it well. In particular, he claimed that he showed them that after adjusting for returns, the order-again rate for a particular expensive item was effectively zero, they asked him to repeat his study for another product, and he wandered off and found work to do for his own team.