Some travel sites (I think Hotels.com?) only allow you to leave reviews on their site if you purchased through their site. That's one way to verify.I would imagine a receipt or bill of some kind, or show a credit card charge to the property(?)i am curious to know how a site such as trip advisor or bandb.com or any of the many many sites that encourage reviews would be able to tell if a reviewer stayed at the place they were submitting a review for.
what would constitute proof of stay?
and that's just the beginning ......
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Also, there are ways to make this work. A site like TripAdvisor could give out unique ID codes that innkeepers could give out only to guests who have completed a stay at their inns. That code could be used when posting a review on TripAdvisor, and it would verify the traveler as having stayed there. To prevent fraud, once a code is used, then it can't be used again. It wouldn't hedge against false positive reviews as well as false negative, but it would be a good thing to have. The trick is how to distribute the codes to independent properties, how to easily integrate it into your technology, etc. I'm sure some folks smarter than me can figure that out.