Keep in mind that both sites are estimates - there's absolutely no way to determine which reviews are "fake" with 100% accuracy. The difference with ReviewMeta is that you can actually see the numbers behind our calculation and even open the hood and turn the knobs yourself.
I also agree that it should be very easy for Amazon to pick up on. I can't believe it's happening. We call this "Review Hijacking" and have a warning that appears at the top of our report if we detect it: https://reviewmeta.com/blog/amazon-review-hijacking/
We've been noticing a big surge in the number of really inauthentic looking reviews - I'm talking 1,000 written over just a few days, 100% unverified, and some obvious manipulation going on with the product versions. Here are a few examples. I just don't understand how Amazon isn't catching this low-hanging fruit.
We call this "Review Hijacking" and have a bit alert that pops up on our report when detected. It's not a bug, it's a loophole that sellers are exploiting. They are taking advantage of the "product variations" feature that's supposed to be used for listing products of different styles together in one listing (size, color, format, etc).
However these sellers are essentially stealing old, expired listings of products and collecting all the reviews associated with them to pump up their rating and review count.
This has been going on for over a year. I really don't understand how Amazon hasn't figured out a way to close the loophole at this point...