The warning written on the wanted poster is obviously very different when shown in the closeup.
The gun held by the dead man on the saloon counter changes position from one shot to another.
When Randy enters the Halfway House to meet Sally, from her hiding place, she tells him to lock the door, which he does. Later, when they hear the Sheriff and his men approaching on their horses, Sally runs to the door and opens it to peek out; she didn't unlock it though.
When Marvin Black talks to all his henchmen, he has his hands hanging. Between shots he appears with his both hands leaned on his hips.
Toward the end of the film, Randy gets shot by Marvin and falls with the horse. First we see him trying to stand up behind a thicket. After he appears faint, with his back on the ground. But when he wakes up, he is with his chest on the ground.
When Randy pulls the wanted poster off the wall in the first scene, the bullet holes are in the poster but not in the wall behind.
The Vollmer player piano shown in the saloon wasn't produced until the early twentieth century.