Feedback Only From Authoritative Sources

This idea is common sense: in systems that try to provide space for public deliberation (like comments) or crowdsourced data (like restaurant reviews), participation can be limited to the parties known to have useful information to share, without losing the value of the system as a whole. Some examples:

1. An eCommerce site could only allow users who have purchased the product through the platform to rate the product.
2. A movie review site could require a user to take a photo of their ticket stub in order to rate the film while it is still in theatres.
3. A restaurant review site could require the user's geo-location match the city as the restaurant they are leaving a review for.
4. A company workplace review site could require the user to verify they have access to an email address with @companyname.com in it.
5. A neighborhood forum could mail users letters to validate that they live in the neighborhood they claim to before allowing them to post.

This list is far from extensive, and it largely draws on strategies that platforms already use today. Extending this idea to any domain is as straightforward as asking "how can we tell (with reasonable confidence) that a user is in our target audience", a question that marketers have a wide swathe of approaches for answering.