The source of a story matters before the story becomes part of your argument.

A story that fits your view slips past the checking you would apply to one that does not. Once it has been repeated a few times it stops feeling like a claim and starts feeling like something you know, and by then it is holding up a position. Finding out later that it was thin means dismantling more than the story.

Check where something came from before you use it, not after somebody challenges you. Ask who is in a position to know and whether anyone else reports it. If you cannot trace it, say plainly that you do not know whether it is true.