Thanks everyone for your responses. As I mentioned, I'm not technical and may have misunderstood some concepts.
I don't think there's anything like this implemented cause there are some obvious limitation. Most businesses have multiple means of accepting payment, which will include fiat and other cryptocurrencies, taking reviews with only one payment as proof will limit the amount of reviews gotten and not reflect the full picture of the service.
There will also be privacy concerns, users will fear their transaction info is being shared with other parties and linked to their review which can reduce their anonymity.
I understand the issue with different forms of payment, but I dream of a future where BTC is widely used as a form of exchange. I also believe that restaurant owners and other establishment owners, that choose to accept BTC payments, are open to adopting a different kind of review system. One that is more reliable and gives more power to regulars, who have had the chance to experience the place at different times of the year, with different staff, food, and circumstances.
My idea for providing privacy is as follows: when a customer pays, the system generates a one-time QR code that proves payment. The customer uses this to leave a review, but the review itself is not directly linked to their wallet address or transaction ID on the public site. There’s no need for users to register with an email, phone number, or real name. Reviews can be left pseudonymously, with only the proof-of-payment as verification. The QR code or token is valid for a short time and for one review only. On the vendor side, as already accepting BTC the wallet is public.
I haven't seen any similar system like this.
If other existing wallets are to be used to pay and verify, it'll need the user to manually sign a message to do the "review eligibility verification". (<-made-up term)
Because it can't be based from the existence of the address or public key in the user's wallet since those are publicly available information
Because otherwise, users can just create a watch-only wallet using those to claim the ownership of the transaction to create a bogus review.
You may even require the actual review to be signed by the correct key for it to be an eligible review.
Only wallets that can sign a message are eligible for obvious reasons and you must provide documentation(s) on how to sign a message using various wallets for those who aren't familiar with the feature.
The problem here is, people will likely skip the review since even the current review system we have now, the majority of the actual users aren't willing to take their time to do the review.
That number will greatly decline if something like a signed message is required to post it. (unless there's an incentive)
I understand. In my initial (and perhaps naive) idea, this would be something off-chain, where possession of the generated QR code serves as proof of a verified payment. I agree that the effort required from the customer should be minimal, no more than scanning the QR code and writing the review. I also thought about incentivization: since payments can be mathematically verified, discount vouchers could be issued after a certain number of reviews, in agreement with the vendors who choose to participate.
If you exclude the cryptocurrency and message signing part, IMO it's kinda similar with verified purchase review on marketplace/online shop website.
It’s exactly the same, but it’s not possible to verify a genuine review on popular review websites, especially for restaurants. I know it’s possible to buy reviews (both positive and negative) and it’s often very hard to get them taken down.
I don’t think this is a groundbreaking idea or particularly innovative, I’m just exploring possibilities and trying to understand more about BTC.
