Amazon and Google really have the same trust problem, just different.

Amazon has so many products that on many of them it's hard to determine if you can trust not only the product is as described, but does the seller plan to deliver you the same thing that's described.  In the end, though, you know Amazon is behind the transaction and it's easy to get your money back.

With Google, there are so many products that appear, from brands you've never heard of, how do you know which to do business with even if it is cheaper?

Separately, it blows me away that more companies aren't investing in a truly trusted, independent content strategy.  At this point, so much friction in the process isn't always how to get the item.  It's what to get, and from who and why?

Amazon keeps increasing share of product searches in the US relative to Google, and recent eMarketer estimates put it around 13% of ad revenue compared to Google's 73%.

All estimates I've seen in the past have given retail-related searches about a third of all searches, and so that may be a natural ceiling for Amazon (in the short-term) but even then it will take them some time to reach this.

Google's margin is Amazon's opportunity, remember.  Don't think Google doesn't know this.