The person repeating a claim should know where it began.

Claims travel further than their sources. Something gets said, repeated, tidied up in the retelling, and by the third pass it sounds like common knowledge with nobody attached to it, at which point it can no longer be checked. Passing it on lends your credibility to a statement whose origin you never actually saw.

Before repeating something this week, ask where you heard it and whether that person would know. Name the source when you pass it along, including the shrug when there is not one. Saying you are not sure costs nothing and stops a great deal.