Currently Google only accepts a XML format to submit Product Review Data Feed. Before doing that, please take a look on Tips below to increase successful rate when uploading review on Google.
To get your reviews accepted in Google Shopping ads, you need to meet the conditions from Product Ratings program.
The most important requirements include:
• Has minimum of 50 reviews across all of your products.
• A Google Merchant account for your ratings to appear in Google Shopping.
• A product must have at least 3 reviews for star ratings to show on Shopping Ads, even though products with less than 3 reviews are eligible to show star ratings on the Shopping property.
• Your AdWords campaign type should be "Search Network with Display Select," "Search & Display Networks" or "Search Network only."
• Syncing ALL your reviews with Google (including reviews with low scores).
• Reviews must follow Google’s content policies.
• Pass the manual approval process by Google Shopping team which can take between 2 to 4 weeks.
• Google does not accept reviews syndicated from other sources (for e.g Amazon, AliExpress, etc.), so product reviews should come from actual customers who purchased the products, as Google mentions in program policy, "Review feeds should be collected and owned by merchants".
As much as this sounds unfair, if you have all 5 star ratings on every single review even if they are 100% genuine you will notice that the feed will be disapproved, Google uses a percentage to calculate the accuracy of the reviews, in combination of cross references your review data with other merchants and 3rd party reviews.
What Google is trying to do is to verify the truthfulness of the reviews.
What You Should Not Do
• Do not write fake reviews
• Do not alter the ratings
• Do not rewrite the content
• Do not submit reviews that promote other products or accessories
• Do not submit reviews of low quality like “Cool, Product…”
• Binary answers