Some shops might want to show only their best reviews in the reviews slider (via the shortcode [cusrev_reviews_slider]). The shortcode does not support filtering reviews by rating. However, you can sort reviews by rating in descending order, so that the best reviews are shown first. Then, the shortcode will display the first N of your best reviews.
To do that, use the following arguments of the shortcode:
Here is a very simple example:
[cusrev_reviews_grid sort_by="rating" sort="DESC"]
The shortcode also supports other arguments. Please see "Review Extensions" tab in the plugin's settings for information about available arguments and how to use them.