An asker can "accept" any answer they like. Taken to the extreme: I can accept the answer that totally misses the point because due to that I learned how to solve my problem. That blatantly wrong answer helped me the most. Unlikely it happens often but nothing forbids I use my accept vote that way.
Answers here are meant to be guidance, written by community members for community members. There is no difference here between users, moderators or SE staff. You can do what you want with the given advice, adhere to it, mend it a bit for your own case, ignore it.
There are a few Q/A's that have slightly more prescriptive guidance and that are those tagged with faq. They capture the overall community consensus on how certain aspects of the site should be used or what approach is expected by all of us from the community at large. Still, most posts are by all kind of users and any FAQs written by SE staff often just summarizes what has been established by the community in the previous 6 to 8 weeks. You better not interpret FAQ posts too much for your own liking, just try to stick to the guidance offered.
The question that are SE staff only are those tagged announcement but they can still have answers from users. Only on posts with a Policy Lock you can be 100% sure that is SE staff territory.
We are all held by the Code of Conduct.
Diamond moderators don't get to set the rules. They work with the community that elected them to be a janitor within the rules painted by the community. And communities evolve, painting new rules, color outside the lines.
We all use our common sense to build together the body of knowledge each site, even this meta site, wants to be. Read questions and answers and apply their intent in your daily use of the site as well as in the interaction with other users.