Even without being paid, unless someone is advertising the product somewhere the reviewer won't know it exists to review. And if the reviewer is being sent free product or solicited directly by the producer, that's still advertising. It may be more trustworthy if the reviewer is strict about not letting the producer have editorial control, but you better believe that the company is sending out free products to reviewers because that gets the product in front of eye-balls just like any other ad. The cost of the free review product is the price of the ad.

It does also happen that people get stuff to review and have to send it back of course.

So the company that can afford to send the most stuff to the most reviewers win?

Sure, but that’s still not free. The company is spending time, money and resources on soliciting the reviews, sending units out, receiving units back and then scrapping or selling those units as refurbs/open box. They’re not spending that money unless they think it’s going to drive sales / awareness. It’s still advertising.

> unless someone is advertising the product somewhere the reviewer won't know it exists

Why? If I need something I search for available options and find them e.g. on the producers web presence. Then I buy one or more and review them.