If they make a bad product do you want more of it, even for free?

Like, reviewers get to the point where companies send them free product for review from a long period of legitimate reviews that get them a large enough audience. It's unlikely they're getting their main profits from free products sent.

Obviously you shouldn't take a single person's review as gospel anyway, but just them getting a review copy of a thing isn't a sole reason to discredit their opinion.

I more meant if you require companies to send you goods to review for your business to work, then you can't be impartial.

If the company is worthless, has no integrity, or is an idiot, no. Blacklisting an independent reviewer for a negative review says to me a company relies on dishonest shills rather than their own quality. "You didn't like that one? Here, try this one." at least takes some integrity.

Let's use the example of power tools. A reviewer is sent a tool, doesn't like it. Switch isn't very good, too heavy, motor breaks. So he produces a bad review, recommends against it. A shit company tries to prevent this guy from talking about them again. A good company says "Hey, will you try our new and improved version?" A company that takes their Ls and even listens and responds to criticism is worth paying for.