Often, principally with new users, it happens that useful or correct answers are not marked as answered. I'm asking if moderators have power to mark answered question by other users. A lot of question are answered but listed as not.
Two different issues:
Questions are considered "answered" (as in not listed under the
unanswered tab) when they receive at least one answer with an up-vote. The original author has no control over that functionality.
The "Accepted Answer" function (the check mark underneath the answer votes):
…is the answer that the author felt best solved their problem. It is not guaranteed to be correct or even having answered the question. It's simply the original author's opinion and their personal choice. The moderators do not have the ability to make that determination.