What Is Likely To Be In A Documentary?

Con-ven-tion

1. A way in which something is usually done, esp. within a particular area or activity.
2. Behaviour that is considered acceptable or polite to most members of society.  

There are several different conventions commonly used in documentaries.

Here are a few:

•  Point of View; bias yet it is mainly clear what the view of the maker is. This is done to get their point across to the audience using strong and interesting premise. This is generally what Michael Moore uses in many of his documentaries to make his point extremely clear such as in Fahrenheit 9/11.
•  Presentation of facts; by interviewing experts on the subject matter and using archive footage and photographs. This is used in most documentaries and factual films.
•  Manipulated editing and framing; to create clear meaning to show the producers P.O.V. This can be disjointed to create suspense by concealing the outcome and choosing when information is revealed. 
•  Poor sound/lighting and Hand Held Camera; to add a sense of realism, like the viewers are in the moment in the constructed interpretation of reality. 'Catfish' uses this in the film to make it a more personal approach.
•  Voice over/presenter; to explain the events unfolding or to put themselves into the situations to make their point known in a drastic way. (See clip above).
•  Music; is sometimes used to emphasise moments and dramatise the events on screen. For example, on make-over programmes when the person is revealed to the changes, dramatic music is generally played along with reaction shots.

Overall, the documentary uses select codes and conventions to convince an audience to take their side BUT more often than not they ensure that the argument is balanced to make it a fair judgement.