The intentions are good, but I see some immediate problems: For one, there is no guarantee that someone on that subreddit will have purchased the same product

The intentions are good, but I see some immediate problems: For one, there is no guarantee that someone on that subreddit will have purchased the same product on Amazon. This is especially an issue because reviews will become more important for products that are more niche or bought less frequently. Secondly, the user base of the subreddit will be small unless you can make a convincing argument for why Amazon reviews are broken. Then you have to get that argument in front of a large number of Amazon buyers. Finally, because of the small user base, this will be easier to game than Amazon reviews because karma is easier to spoof than buyer reviews. Someone could become a big fish in the small pond of the subreddit and influence more purchases. It might be a good idea to reach out to some consumer watchdog groups to help with getting some traction under this project