Amazon has a program (Amazon Vine Voices) that enables sellers and brands to send select customers pre-release items for review before the product goes on sale.

Amazon has a program (Amazon Vine Voices) that enables sellers and brands to send select customers pre-release items for review before the product goes on sale. Sellers/brands can also do that outside their sales platform. Note that these are almost always "free products in exchange for review" and are supposed to be appropriately disclosed.