So google basically lists two types of markup in Google search results in listings in their guidelines:
A snippet from a longer review article that a single editor has created, curated, or compiled for a publisher.
A rich result (previously known as a rich snippet) of a review or rating markup from a review website, usually an average of the combined rating scores from reviewers. Review snippets appear in Google Search results either under the search result or in the Google Knowledge Cards.
Authoritative human editor(s) must create, curate, or compile content for critic reviews.
Profanity and vulgar language are discouraged.
Reviews should be appropriate for a broad and diverse audience. Consequently, reviews containing vulgar or profane language may be ineligible for use.
Refer clearly to a specific product or service. Do this by nesting the review or ratings within the markup of another schema.org type—such as schema.org/Book or schema.org/LocalBusiness —or by using that schema.org typed element as a value for the itemReviewed property.
Make sure the reviews and ratings you mark up are readily available to users from the marked-up page. It should be immediately obvious to users that the page has review or ratings content.
Provide review and/or rating information about a specific item, not about a category or a list of items. For example, “hotels in Madrid,” “summer dresses,” or “cake recipes” are not specific items. See also our structured data guidelines for multiple entities on the same page.
No reviews are shown for adult-related products or services.
Single reviewer name needs to be valid. For example, "50% off until Saturday" is not a valid name for a reviewer.
Ratings that don't use a 5-point scale: By default, Google assumes that your site uses a 5-point scale, where 5 is the best possible rating and 1 is the worst, but you can use any other scale. If you do, you can mark up the best and worst ratings, and Google will scale that to the 5-star system used in rich snippets.
So like, translation: You can markup schema for reviews on your website that are original and not simply duplicated from third-party review websites like Yelp, Google map reviews, etc. Damn lol. But it is okay to have these reviews on your website if you don’t do structured data markup on them.
So what this means for all those plugins that enable you to get “rich snippets” on google reviews and other reviews on your website, are actually going to be penalized and minus your SEO rather then actually giving you any benefit lol. So gotta say goodbye to any of those plugins and have them removed today.