How Good is the Google Agency you Want to Hire?

If they carry sound principles, have lots of reviews, and have consistent statements on social media (They don't sell new systems every few months) we can be more confident that they are "good."

Public data includes reviews, blog posts, social media posts, and interviews, where the owner, or a representative of the business, has publically showcased their methodology.

Very heavily. Unless we have an employee with direct experience with the marketing agency, this is usually the biggest factor.

We have 3 method to evaluate agency results. The first, our prefered method, is by having someone from our staff contact the agency directly, and look at results on a Zoom meeting. We go through all results, good and bad. The second, is an insider. This usually is more difficult, since knowing if the employee is reliable can be tough, and we supplement this with one of the other two. The third is simply customer reviews. If we see reviews on websites like Trustpilot, or by contacting/running ads asking for reviews, we can get a lot of data.