You are right, my suggestion involves the lowest hanging fruit where one can purchase unlimited positive or negative reviews from unrelated parties.
I can google a far away barber who has accumulated 17 reviews over the last 10 years. Google then allows me to shit talk the guy for the world to see. 2 minutes of effort and its free! They get to carry it around like a badge of shame forever.
You should give me a discount or ill post a negative review and unleash the roaches on your hotel. It would be rude if you didn't.
edit: I think a digital ID would be useful for real reviews.
This does not solve the problem. Fake reviewers often purchase the product on paper.
Behind the scenes, the seller may not even ship and instead buy fake shipment tracking from the shipping company.
This is much more complex than what you are thinking.