I work in business and I have a vendor providing a service and product for me.
The vendor is self-reporting that what they are providing is correct and accurate (versus a third-party auditor validating that it is correct and accurate). "Yes, we are doing a great job, we promise! All of our work is done 100% correct, trust us on that!"
I'm looking for the idiom/metaphor I've heard before for this scenario, where someone self-evaluating their own work.
This is not the metaphor, but it would be like if a student wrote an essay and self-scored it an A+ and gave it to the teacher to enter into grade book.
The idea is that someone independent of the person producing the item has to evaluate its quality, and one cannot simply trust the producer to truthfully grade herself.