It’s explicitly against Amazon’s ToS to incentivize reviews, or write/modify reviews in exchange for any kind of compensation. This includes the typical business card included in the box with the product pleading for 5 stars and promising “free gifts” or store credits. When I still used Amazon, any time I got one of those it was the only thing I mentioned in my review.

I don’t know if anyone actually meaningfully enforces this, but quite a few things I’ve reviewed in such a way seemed to disappear from the site more quickly than usual.