I know that I recently deselected a Best Answer to a question I posted. The question had been posted for a mere hour, and there was only one responsive answer. A person with very few Wikitree contributions and few G2G points selected a Best Answer. It was probably an error on the part of the person making the selection, not realizing what she was doing.
I believe that, once a Best Answer is selected, others are discouraged from answering the question. Although the answer she selected may be the best, I believe that Best Answers should be selected by the person who asked the question, or at least by some one who has knowledge of the subject, and enough time should be given to allow the community to see the question..