Here's our troubleshooting video explaining some things to look out for if your Google Seller Ratings aren't showing up in your ads.
As Google Seller Ratings are an automated extension, you aren't able to change any settings or have any control over whether they show or not. Assuming you've met the criteria outlined above, there might be a few reasons why they aren't showing in every search.
1) You're performing multiple searches from your own IP for the same keywords
If you spam Google search over and over again looking for your ads or extensions, Google will stop showing them to you, so don't be over-zealous in checking if they exist. If you really must check, then ideally you'll want to use Incognito mode in Chrome, but even then you may face issues.
Google may cache the results shown to you if you perform the same searches over and over again so this may be another reason why your seller ratings don't show.
If you have checked the eligibility link for your domain on Google and everything is good to go, then there isn't more you can do.
2) Google is deciding when to show your Seller Ratings
Time of day may be a factor in Google's decision to show your seller ratings, so if they're not there, try again a bit later on. Vary your keywords also, because different keywords have different intent.