Definitely not, long-term. But plug it into a product manager's A/B test and I guarantee it boosts things short-term.

What's to boost? The customer would have selected the better option and been more satisfied, and Amazon would have brokered the deal either way. They still need their hammer.

Maybe in A/B tests, customers who see a product with 4.9 (fake) stars are more likely to click Buy than customers who see the same product with 4.3 (honest) stars?

My theory is that they have metrics for selection they are trying to optimize. If customers only bought the 10 best of any item, how could some PM get a promotion for increasing phone charger selection 100x?