We haven't encountered this problem yet, and believe most developers are decent enough to honestly rate a package based on their experience, as opposed to using it as a leverage.
Few things we're thinking about:
* Allowing maintainers to flag such reviews (for our review)
* Allow users to upvote/downvote reviews, and flag bad behavior (spam, extortion) to stir away bad players.
* Allowing maintainers to publicly to reviews
* Gathering enough data (about review and other previous user reviews) to conceal "bad" or non-useful reviews, in a similar manner to other platforms.
What do you think? Do you have any other suggestions?
E.g. React has a huge resource pool and people are getting paid for development, while some (most?) packages are single dev with no funding.
Perhaps making this kind of metrics visible would introduce some humility for people pressuring latter maintainers.
One similar thing we were thinking of is giving maintainers the platform to easily provide paid support if they want to. Not sure about that one either, although I know some companies/people make money from providing support for OSS.