Users are to assume good faith whenever a user makes an edit as it was probably to help the wiki, not to vandelise it. Since both users and unregistered users can edit, we must assume that most people are out to help the wiki and not to hurt it. When you are positive a user has made a nonconstructive edit, feel free to correct it.
If the user has made a mistake, correcting it without slandering or criticising them is a must. If the user has made these faults multiple times, informing the user of the faults in question is recommended, but should not be about anything other than informing of these faults or mistakes. Whenever you are disagreeing with people over specific statements or structure of the site, the users involved are to follow the Dispute policy.