Revealing mistake: When Sam is going back to Oda Mae's, when he's walking toward the door his reflection is visible walking the same way, though he's not in front of the window at an angle this would be possible for a few seconds. I don't know exactly what could cause on the filming side of the mistake, just that there's no way the reflection would look like that.
Revealing mistake: When Carl is accessing the recently closed account, he moves to a second computer to attempt it. Look at the screen before he gets there. It already has the "account closed" and account information blinking on the screen. It's highly unlikely that he tried the account on that computer before, because when he first leaves his chair he looks around the room for an open computer.