How did you reach this conclusion? OP never asked for unethical ideas. I interpreted "but you'd not talk about them" as "not to attract competition", not "unethical or illegal"
BTW, writing fictional reviews for money is not only unethical, it can be illegal too
I decided to put it out there because it was exactly what the OP asked. It’s something I would rather not talk about. Whether you think it’s unethical/illegal is up to you of course.
For what it’s worth, i am no longer involved with this today.
how/why illegal?
Google Search should be smarter about these kinds of practices.
Unfortunately, this is a very hard problem to solve. Google would have to be aware of GP in advance, would have to know their nature, and would have to know that they weren't someone who was given access to the new products early to review. If anything, it would have to be up to those companies selling the product to look for early reviews but even then, they'd have to make sure that GP wasn't a legitimate reviewer
Why?
A product review for something they only heard about? They didn't actually buy the product, try it out. Its lying and misleading visitors.