Amazon paid reviews:
http://www.cracked.com/personal-experiences-2376-i-get-paid-to-write-fake-reviews-amazon.html
https://techcrunch.com/2016/10/03/amazon-bans-incentivized-reviews-tied-to-free-or-discounted-products/
https://www.amazon.com/forum/top%20reviewers?_encoding=UTF8&cdForum=Fx2Z5LRXMSUDQH2&cdThread=Tx1HZGC6589PMFD
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"The process will work as follows:
Upon your confirmation, we will send you a 99% discount coupon code and you will purchase the product (cost will be 40 cents) on amazon via the link above.
Once you receive the product you may test it if so inclined and then post a 4-5 star review on Amazon according to your level of satisfaction. The review must be of course relevant to the product and posted within 7-14 days of receiving the product.
You will then send us confirmation and or a link to the review you posted. Following your review we will send you a $5 payment (paid via paypal)."
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I've seen this on camera lenses.
Almost but not quite identical (ESL) wording, on multiple lenses, across several different camera types.
Really? You have the relevant Sony, and Canon, and Nikon, and Fuji camera bodies? Riiiiight.
So the 'reviewer' gets the product for free, gets paid $5, and then gets to sell the 'free' item, as 'New In Box'. Winning!