Amazon seems to encourage this. I ordered a pair of cheap wireless headphones that were highly rated. I get them and they are crap. But, included in the package is a flyer offering an Amazon gift card for more than I paid for the headphones if I gave a 5-star review. My integrity is worth way more to me that that. So I leave a one-star review with a picture of the flyer, hopefully someone else will see that and realize the reviews are fake. Amazon rejected my review because it didn't meet their guidelines since it mentioned "Reviews given in exchange for cash, discounts."