According to Facebook, only Business Pages that allow Facebook Recommendations will show a rating and a Business Page may not have a rating if the Page has not received enough Recommendations.
However, when a customer recommends a business, they have the option to choose which audience to share that recommendation with. So, if a Facebook user posts a recommendation and selects 'Friends' as the audience who can see that Recommendation, then only their Facebook Friends are able to see it; you won't. It is only the Recommendations that have been posted for the 'Public' to see, will it appear for everyone to view and this will be included in your own Business Page's overall rating.
If you discover a negative Recommendation or review on your page, unfortunately, you cannot delete it (or at least, you cannot delete individual reviews). The platform doesn't allow you to delete a Facebook Review the way you can delete comments or content. Instead, you would have to report the review or recommendation that does not meet Facebook's Community Standards.