Yes, plus you are missing that each reviewer should also submit proof of purchase only visible to the company hosting the review and for validation purposes.

Right. The business owner choses whether they want to participate in any review. For each platform the choose to particpate they print a onetime code on the receipt, valid only for a day or 2. Only using such code a review can be posted. That should solve most problems with fake reviews by outsiders. But how to prevent fake reviews produced by the business themselves? That sounds harder to solve.

Well, in practice even the proposal with the review tokens wouldn't work for years. How would a small business get them integrated into their cash register? More complicated than putting a sticker "Rate us on trip advisor" to the front door.