Another privilege you can add is that high point users can pick best answers. If the best answer isn't actually the best answer, they could change it. You can obviously pick how many points because if you let anybody you would have "best answers" changing all the time.
Basically what speed freak said:
The Editors and Pokemaster can pick best answers, Experts used to be able to but Pokemaster decided that the regular people should choose for themselves.
In your profile you can see all the questions you asked so you can go back and choose best answers later if you like.