“You can’t BS a BSer” (“You can’t bullshit a bullshitter”)

“You can’t BS a BSer” (“You can’t bullshit a bullshitter”) is sometimes used in political arguments. The cynical premise is that all politicians are BSers, so that one can’t easily BS them. “Don’t bullshit a bullshitter” has been cited in print since at least the early 1970s.
 
A similar phrase is “You can’t con a con man.”
   
 
Google Books
The Set Up
By Robin Moore with Milt Machlin
New York, NY: Pyramid Books
1975
Pg. 64:
“Don’t bullshit a bullshitter, son,” the man in front of him said.
 
Google Books
The First Lady:
A Novel
By Ron Nessen
New York, NY: Playboy Press
1979
Pg. 221:
“Never try to bullshit a bullshitter.”
       
Google Books 
Bill Haley
By John Swenson
London: W.H. Allen
1982
Pg. 114:
I got along with him pretty well because you can’t con a con man and you can’t bullshit a bullshitter.
 
Google Books
End of the Rainbow
By Mary Ann Crenshaw
New York, NY: Golden Apple Publishers
1985, ©1981
Pg. 153:
They are fond of saying, “You can’t bullshit a bullshitter.”
     
Google Books
Skyscraper
By Karl Sabbagh
London: Macmillan London
1989
Pg. 165:
As Schubert himself remarked on another occasion, there was value in this approach: “You can’t bullshit a bullshitter.”
   
Google Books
You Can’t Put No Boogie-Woogie on the King of Rock and Roll
By Lewis Grizzard
New York, NY: Ballantine Books
1992
Pg. xii:
And, “You can’t bullshit a bullshitter.”
   
Google Books
The Best American Sports Writing 1993
Edited by Frank Deford and Glenn Stout
Boston, MA: Houghton Mifflin Harcourt
1993
Pg. 120:
“You can’t bullshit a bullshitter.”
 
Google Books
The Southerner’s Book of Lists
By Jim Erskine
Gretna, LA: Pelican Pub. Co.
1996
Pg. 12:
“You can’t BS a BSer.”
 
Google Books
What They Don’t Tell You in Schools of Education about School Administration
By John A. Black and Fenwick W English
Lanham, MD: Scarecrow Press
2001
Pg. 97:
You’ve heard the saying, “You can’t BS a BS’er,” but we don’t believe it.