In the Google search results the listing correctly shows the price and 'in stock', but it doesn't show the reviews and rating. When I check the markup in Google webmaster tools it shows 2 errors with every review:

Also for each individual rating Google gives an error that ratingValue is empty.

How could this be solved?

Thanks,
Ruben

All questions about this in Woocommerce support and other places like Github seem to say that the theme should provide the correct code. Or you should manually add it to the theme. For example here:
https://github.com/woothemes/woocommerce/issues/10314

http://stackoverflow.com/questions/14227121/how-do-you-add-the-star-ratings-for-products-in-woocommerce

The theme seems to provide almost all necessary schema markup except the correct review count and value. It would be a great help if you would be able to take a look.

Here is how it should be provided. http://schema.org/AggregateRating
In the theme code both ratingValue and reviewCount seem to be missing on a product level. And ratingValue is missing on individual review level.

If I check a theme built by Woothemes (http://demo.woothemes.com/storefront/product/flying-ninja/) the markup code is provided.
https://search.google.com/structured-data/testing-tool/u/0/#url=http%3A%2F%2Fdemo.woothemes.com%2Fstorefront%2Fproduct%2Fflying-ninja%2F
vs
https://search.google.com/structured-data/testing-tool/u/0/#url=https%3A%2F%2Fwww.ruconnected.nl%2Fkabels%2F15-hdmi-kabel.html (which gives 45 markup errors, all in the reviews)

It should be an easy fix, but I'm afraid to break the theme's code.

Best,

Ruben