I don't think it was so much faith in their ranking systems, as a fundamental understanding from customers (including me) that when I searched for something on there....let's say a laundry bin for the closet...that what would show up would be what best matched what I asked it to search for based on all the other people like me who searched for laundry baskets that would fit in the bathroom closet.
The results might be out to lunch, but it will reflect what other people who searched for what I searched for wound up buying after a thousand iterations of this process.
Now, when I search, I can't trust that. I will have to carefully evaluate those results to see if what I'm really looking for is somewhere on page four because the ones on page 1 through 3 give Amazon 2 cents more per transaction.
That's the thing. As a prime member since 2001 who has bought literally thousands of things...embarrassing, yes...I've always had faith that the "wisdom of the crowd" was what the algos used, not the profit margin. I'm shifting my purchase as much elsewhere as I can now.