We appear to be getting a splurge of skeptics questions in the form of "My friend says...", "I heard...", etc. where the only evidence that a claim has been made is the person saying they heard it. Some are commonly known claims, but others are definitely things I've never heard before. I strongly suspect it's just an effort in most cases to phrase things properly to get an answer to a question, and has nothing at all to do with skepticism.
So the question:
There are some commonly held "common sense" things which one should be skeptical of, but may be hard to find a claim to link. How do we draw the line?