Check the account history of the source. Two red flags are: the number of posts and how long the account has been active. If it claims to be a well known source (like CNN or CBS) and only has a few short posts in it's history, that is a clue. If it's a well known source and the account has only been active a short time, that is another red flag.
Nearly all of us have been taken in by a video that was later found to have been doctored or faked. It is fairly easy to edit a video so that it looks like you made the basket or the hawk picked up the snake. Here are some of the most famous faked videos that fooled millions.
Some tips on how to tell if a video is fake:
