How would you even implement a verified purchase? For a hotel maybe you could forward an itinerary (which can be faked) but there’s probably no receipt for a random taco stand that only accepts cash. Granted the latter does not care as much as the hotel but whatever they do would need to cover everybody.
After thinking about this problem for... umm... 30 seconds...
Allow users to write reviews, and then send a message to the hotel owner saying "X has posted a review of your business. Do you accept that X was a guest on X date?"
The hotel owner is forced to verify the stay before he gets to see the review.
Of course he'll know all about the outliers who had a bad experience and complained at the hotel and might want to lie about the guest staying, but such guests are usually very motivated and willing to prove their stay with receipts, photos, etc.
With a receipt system to authenticate real customer and an opt-in inscription to the service by restaurants/hotels, it could make it.
It could be linked to an order/invoice number the owner could check or enter in the system when the client check in or check out. The client would then be required to enter that number to authenticate he's a real consumer.
That's not how Yelp works, though. It's not opt-in or even opt-out. I'd guess most businesses reviewed on Yelp have no relationship with Yelp.
And ones with primarily bad reviews (which may not be their fault: cheap motels in particular seem to attract bad reviews from people who expect too much for the price) could just refuse to acknowledge any reviews.
Plus I think users are attracted to the illusion that the business doesn't know who they are. People would be less inclined to post reviews if they knew they'd be emailed directly to the business owner for sign off.
How would Yelp know if you made a purchase? You’re not buying anything through them. Lack of a verified purchase describes pretty much every review long before there was a Web although there were of course gatekeepers like newspaper editors.
Without a verified purchase, why would anyway take the review seriously?