Many variations of this “old saw” appear with a search for examples.
Maybe we can collect some favorites, or, better still, come up with some of our own.
All seriousness aside! 
– One instance from believe nothing of what you hear, and only half of what you see | Encyclopedia.com
“90% of everything is bullshit”
“73% of all statistics are made up on the spot”
“Hello,” he lied.
“Lies, damned lies, and statistics” - Twain/Disraeli/Other, Not Specified
People say believe ha-alf of what you hear, and certainly none of what you see.
But if it’s true, please tell me dear, 'cuz you mean that much to me.
“If you open your mind too much, your brain will fall out.”
50% of the people will believe this, 50% of the people won’t. The other 30% don’t really care.
Who do you believe, me or your lying eyes? 
It has to be true if its on the TV. Its, like, the law or something.
“I wouldn’t have seen it if I hadn’t believed it.”- Marshall McLuhan
“Half of what you read is bull, and the other half is shit.”
“I don’t know half of you half as well as I should like; and I like less than half of you half as well as you deserve.”
– Bilbo
Knoll’s Law of Media Accuracy: Everything you read in the newspapers is absolutely true except for the rare story of which you happen to have firsthand knowledge.
The Daily Mail Song. Beautiful.
“Brussels politicians want to stop us drinking English ale,
it’s absolutely true because I read it in the Daily Mail.”