If companies don't like his reviews, they'll stop sending review units. That hits both in the pocketbook and the race to be one of the earlier reviewers of a new product. Reduced conflict, perhaps, but not none.

If companies don't send him review units then he just buys them retail. He has already done this for many products.

Yes, I'm aware. That's less money in his pocket, and less ability to have the review be available on or before the product launch. There's still some conflict of interest, even if it's lessened.

Only purchasing review units at retail would remove this conflict.

Incorrect. He can then return them.

Depends, if someone is popular you can't afford not to have them review your things. A a certain point a bad review will still generate more money than no review at all. Few reach that level though, most reviewers don't have that much following.

This presupposes that companies think their products are bad. If you have (what you believe to be) a good product, you definitely want DC Rainmaker to review it. I think this is a reasonably general point across industries - companies want to get their products into the hands of the most reputable reviewers.

In DC Rainmaker's case it is probably the opposite. A fitness product not reviewed by him is a bad signal.

Any serious publisher has that policy. Here's Wirecutter's (NYT) take on it: https://www.nytimes.com/wirecutter/blog/yes-i-work-at-wirecu...