Amazon has a problem with fake reviews and it seems they are ok with it. I bought a replacement screen from Amazon and it wasn’t working properly. I thought I did something wrong so I contacted the seller/manufacturer and they told: oh yeah, it‘s defective, we‘ll just give you your money back. I agreed and then the person said „cool, now in order to process your request, please click these buttons on Amazon” and they…
If your neighbor recommends you a crap lawnmower, he'll have to explain to you why he thought it was good. You can ask him questions and compare his motivations to yours. He'll also end up living next to a badly mowed lawn if he doesn't put some work into it.
The seller has every reason to pay people to write good reviews. He doesn't even need real people, it's the internet and you can invent people, complete with their own unique photos and profiles.
Basically, honesty is expensive and cheating is cheap. Why would we trust it?
My personal experience with Amazon is that it's the shop to go to for stuff that is ok if it is broken. If I buy a cable for £10, and there's a 10% chance it's faulty, it's not a huge problem for me. The other use case is where the guarantee comes from the brand. I'm not sure why but I tend to think if I buy an iPhone on Amazon, it will be the genuine thing from Apple, and I have history with Apple apart from Amazon reviews.