Sometimes I realize mid-assertion that the thing I'm saying isn't really to be trusted as much as my listener will be likely to trust it without further details. I usually compensate by making a weak joke: "...and I know that's true because I read it on the Internet, and as we all know, decent web design signals infallibility!", or "So I am told by my friend X, and gosh, she's always been a Libertarian, so I have no reason at all to be suspicious of her statistical claims about gun violence."