When Banacek picks up the black phone to call Betty Janus, he tucks his left hand under his belt. When the shot changes, his hand is at his side.
When Banacek and Linda are flying to L.A., the close up of them in the plane shows a window divider in the middle of the front window of the plane. But after landing in L.A. the view of the plane shows that the front window is a single window with no divider in the middle.
The stacks of bills were much too big to represent the amount of money that is supposed to be there. Each of the five stacks were
supposed to be composed of two hundred $1,000 bills (5 x 200 x $1,000 = $1,000,000). A stack of 200 bills would have been smaller than a half ream of paper, and much smaller than the stacks of bills seen in the display.
When Linda and Banacek get the plane to fly to Los Angeles, someone taxis it to where they pick it up - but she never does any preflight checks. Even though (theoretically) someone could have preflighted the plane for her, as a pilot she would never have made an assumption that the plane was preflighted before taking off.