Your account will be charged only for setting a task.
The cost can be calculated on the Pricing page.
Setting Google Shopping Reviews Tasks
This endpoint will provide you with a list of reviews for any product listed on the Google Shopping platform.
The returned results are specific to the gid specified in a POST request. Learn more about the gid parameter on this help center page.
Note: your account will be charged for every 10 reviews returned in the items array, e.g., if you specify "depth": 11, you will be charged as for 20 reviews.