The easiest way to break it down is a guy hired as a reviewer by a company, for example, a product reviewer for a magazine. The magazine gets sent free products to review which they then get their employee to review the product. The manufacturer doesn't pay him to do the review, his employer pays him to do his job, ie review products. The reviewer doesn't get to keep the product after the review is published, nor does he get any of the proceeds if the product is given away.

A YT reviewer on the other hand gets free products to review, promote, advertise, create hype, influence sales and gets paid for it by the manufacturer. It's in the best interest for that reviewer to keep on the good side of the manufacturer or chances are he won't be getting free products to review from that manufacturer in the future. I'm sure you've seen that scenario happen among the big reviewers.