Ever heard the saying
You can't cheat an honest (man/woman)?
This is why they were so easy to fool (they wanted to believe it). They here being anybody/everybody at CBS. Even if Rather was in on forging the documents, everybody else had to WANT the story.
"You can't cheat an honest (man/woman)?"
The rest of it is "never give a sucker an even break"
Rather/Sucker