Some users like to use the simple Rate My Post plugin that can be downloaded from wordpress.org free of charge. Here is how you can configure an AggregateRating within SNIP.

First of all you need a (Global) Snippet that can inherit an aggregateRating property. The Product schema, for example.

Now do the following:

1. Add the aggregateRating property to your schema.
2. For the “Field Type” choose “AggregateRating” that can be found under “Related types”.
3. SNIP will then load some sub-property for the AggregateRating schema. You should now do the following:
4. For the bestRating property, choose the “Field Type” of “Direct text input”. Enter “5” (without the quotes) to the text field that appears.
5. For the worstRating property, choose “Field Type” of “Direct text input”. Enter “1” (without the quotes) to the text field that appears.
6. For ratingCount, use the Field Type “Post meta field” and enter the following value into the text field: “rmp_vote_count”.
7. For ratingValue use the Field Type “Post meta field” and enter the following value into the text field: “rmp_avg_rating”.
8. All other properties are not needed. So if SNIP loaded some more property, just delete them. For example itemReviewed and reviewCount.