A few things i'd like to say about the conversation above:
Free review units != sponsorship: Sending a product to a reviewer is not like paying the reviewer. They usually cant sell the product either. They get sent the product in order to make a video and give their opinion. If they think the product is bad, they're free to say so. Of course companies like nvidia can sponsor Linus's videos, but that will not be a part of a review. It's either a pre-roll ad or product placement.
Linus can't get away with lying about a product: He's not the only person reviewing it either. If the product is shit people will find out one way or another. Whether that's other reviews or feedback from consumers who bought the product. If Linus makes a positive review about a crappy product, people will find out and he will not get away with it.