Seller rating frequency
What is the average impression frequency of seller ratings? How often they show up? Does anyone feel that they show up lesser (frequency) than the regular extensions? Why they show up lesser?
There is no specific answer to your questions as seller rating impressions depends on multiple factors.
Since it's an automated extension type, you don' t set up seller ratings or control when they show. And Google may not show seller ratings when the underlying feedback is unrelated to what's being advertised in a specific ad.
But you can take steps to make seller ratings more likely to show with your Search Network ads - Find more information here - https://support.google.com/adwords/answer/7233787