Just before Larry goes on air during his first TV appearance, the straw in his mouth disappears between shots.
In the scene where Marcia is recording Larry in the jail, she surreptitiously records him as he is warming up. When he announces that he's ready, she reveals the microphone and then stops the tape. However, when she is replaying the tape, Larry can be heard asking if she had the recorder on the whole time.
The Variety cover announcing Lonesome Rhodes's on-air meltdown not only misspells his last name as "Roads" but is also dated "November 21, 1956", which is well before the other dates in the movie (e.g., earlier he was picking Miss Arkansas Twirler 1957).
At the baton twirling contest it is obvious (during the long shots) that a stand-in is twirling the baton for Lee Remick.
When Larry and Marcia have a conversation on his balcony, he turns toward her, but when the camera cuts to Marcia, his reflection in the glass door behind her shows him looking away from her.
"Lonesome Rhodes" is in jail for a week for being drunk and disorderly. When he's asked to sing a song, he pulls his guitar out of its case along with a visible bottle of whiskey. It's highly unlikely the police wouldn't have searched his guitar case as a matter of safety. (He could have had a gun in there.) Certainly, they would have found and confiscated a bottle of "hooch", especially from a prisoner who had been charged with drunkenness in the first place.
The initial scenes were set in Piggot, Arkansas. When Lonesome leaves for Memphis, the townspeople go to the train station to wish him well, but one of them holds up a sign in which they've misspelled "Piggot" as "Pickett".
In the protest scene outside of the mattress store, protesters set fire in a trash barrel that has the letters D.S.N.Y., presumably for "Department of Sanitation of New York". However, this scene is set in Memphis.
When the Sheriff escorts Marcia into the jail holding cell, he welcomes her to the "Tomahawk County Jail". However, in the exterior shot just prior the cornerstone of the building plainly reads "Clay Co." That's because the exterior was shot at the Clay County Courthouse in Piggott, Arkansas. There is no Tomahawk County in Arkansas.
Lonesome Rhodes does not realize that Marsha has restored the audio when he goes off on his extended tirade against the viewers of "The Cracker Barrel." However, he makes a point of looking directly into the camera when mouthing off. He should have realized that anyone who could read lips would understand what he was saying.