They do, but it's not a job nor is it compensated except by delivery of the products. It's called the Amazon Vine program. There is also something called the Early Reviewer Program which is different. Sellers opt in to the ERP for new products. People who participate in the reviews sometimes get a tiny incentive from Amazon.
... and for some reason, Vine pretty much means "all the stars, all the time", so that's not "testing", that's just buying a 5 star review from a "verified" account.
I don't think most people who aren't Vine reviewers are happy with how it works ('cause they get free stuff). I have seen Vine reviewers leave bad reviews, and I know because I've been yelled at over it.
Yeah, it's not 100%, but it's far north of 95%. When I see Vine reviews, they are pretty much always 5 stars, even on products that have very mixed reviews from verified purchases. When I view the Vine-member profiles from those reviews, it's 20-30 five star reviews for every 1 star review. I can't remember ever having seen them give 2, 3 or 4 stars.
My impression is: you pay, you get 5 stars. They buy a product themselves and didn't like it, you get 1 star.
That's rather how a lot of Amazon reviewers are. Vine-rs are also now the only group of reviewers that can officially review products for free. Naturally when you are getting something for free, it's hard to really take value into account. A lot of 2-star $100 products might be "5-star" if you pay $0. That's something Amazon recognizes in its own policies towards normie non-Vine reviewers.
Absolutely, but it makes Vine-reviews useless to me. I'd take the product for $0 and be happy, but they aren't offering it to me for $0, so some review that's essentially "it was free, it's fantastic for something that was free" isn't relevant.
Maybe it's just not an issue for most people because they don't know that reviews could be bought, so any and all reviews are great for making the sale from Amazon's perspective. If the minority that chooses to shop elsewhere grows too large, they can always make a dramatic gesture, punish a dozen people with fake reviews and donate to a children's hospital.
It's essentially an ad, not a review.