There are in fact reasons why anti-Russian countries would undertake this themselves, or even just make up the story. The reasons being that it drums up support for their cause, draws lines that people have to be on one side or another, etc.
Ultimately, this is an epistemological question - what do we know? And the only things one can say one knows, is stuff you have personally verified. After that, you are believing and trusting - the news, the footage, your governments, etc.
Is trusting those sources really an acceptable basis for any autonomous individual to proceed?