I would suggest adding Fakespot to your process. They analyze reviews and will spot the ones that are most likely fake, and then adjust the rating of the product accordingly.
Fake reviews are paid for by sellers shifting tat that Amazon themselves will not sell (because someone in that bit of Amazon still cares about quality). If Amazon themselves wanted to add fake reviews they could easily do it in a way undetectable by Fakespot etc.
Fakespot in particular is a business with a business model, and that is (I think) all about ads and affiliate links. Just a guess, but probably VC-funded with a pressure to actually make a profit somehow. I am thus not their customer, and their incentives may not always align with mine so it's hard to trust them.