You're right they wouldn't do it with money directly as there are other ways of doing it which carry just as much water morally and are just as financially impacting/effective (business-wise).
I've always had an issue with the whole system of online "professional reviews". As others have mentioned here in this thread if a reviewer gives a review that a company doesn't particularly like ,they just won't send next year's model to that reviewer. Which is punishing honest opinions or feedback. Most people are openly willing to admit that although money or goods may not change hands(in some cases) between reviewer and manufacturers, there are repercussions for both good and bad reviews which vary depending on what company you're dealing with. In my opinion the fact that money isn't directly given to the reviewer is moot(speaking from a business perspective) ,because by cutting off further review samples because of a bad review your essentially cutting off the ability of that reviewer or tech site to remain relevant and therefore disabling their ability to generate income/revenue.
I just don't trust the system of reviewers as a rule of thumb nowadays, at least not beyond maybe 5% when it comes to forming an opinion or making a decision of a purchase, or any other reason. All too often I've seen people who do reviews for tech sights often have items for sale regularly and you have to wonder where they're getting a constant regular flow of the high-end components in tech gear. it makes a person wonder if there is and some wrongdoing going on there or at least unethical activity or business practices.
All in all, imo its a field that is sketchy as f@ck, and light on trust. Which is why there's a million unboxing & reviewing channels on YouTube , loaded with people who have absolutely no moral qualms with putting their " seal of approval" on a pile of crap for a couple bucks or a free engineering sample to keep. There's absolutely no time in life where it's not smart to keep your wits about you, always be as informed as you can, and take everyone else's opinion with a grain of salt