I would agree that there's absolutely a difference between a review for a product you've used or helped support and a review written because somebody on HN told you to write it.
It really does feel like at least half. I went to buy an iPhone 7 case and they all had 50+ 4.5 star reviews... before the iPhone 7 had shipped. I filtered one case with 40+ reviews to "Verified Purchases" only, and only a single review was left.
But nearly half of Amazon reviews these days are paid advertisements by the seller in my experience.
And while I think you should never write a review for a product you've never used, if you've:
1. Supported or used one at work
2. Had to make purchasing decisions at work, done research, and chosen a competing product
3. Helped a friend or family member with one
Then go right ahead.