We have a number of safeguards.
First, we have automatic speech filter to make sure that the reviews adhere to the guidelines for civil speech.
Second, we have a built-in "comment" feature underneath each review. If you feel that a particular review was unfair, simply click on "comment" and feel free to clarify or respond to the review. We encourage you to engage in dialogue with your reviewers.
Third, this is an opportunity to ask the people who know your work to write about their experience with you. (See #2 for tips on how to encourage reviews.)
Fourth, a number of nonprofits have found that constructive criticism provides useful feedback that can be used to improve operations and implement new suggestions.
Finally, in the world of online reviews, readers understand that there are going to be different perspectives and they don't expect any product, service, or organization to be perfect.