Google Business Profile API

Google Business Profile API
Access all reviews (not limited to 5) — but only for locations you own or manage. Requires OAuth2 authentication.
Key Endpoints
Endpoint
Purpose
accounts.locations.reviews.list
All reviews for one location
accounts.locations.batchGetReviews
Batch review extraction across locations
Returns: reviewId, starRating, comment text, creation/update timestamps. Free for business owners.
Google Takeout Alternative
Business owners can download all reviews from their GBP as JSON via Google Takeout (free, official).
Source: Business Profile API — Review Data