Corrected entry: During the main scam of the movie, Steve Martin poses as a wheelchair bound Naval Officer. The only problem is that he wears an Army dress blue infantry uniform with the rank of Corporal. Clearly neither naval nor an officer.
Correction: First, this is in Europe, therefore Americans, and the uniforms of their troops, are not likely to be well known by all the civilians, Second, it is established early on "Freddy, you are a moron." Third, well in a rare moment of foresight, Freddy could be planning against getting charged with impersonation of an officer, by technically dressing as a common soldier (lesser penalty), though in typical Freddy fashion, that probably wouldn't work.
Corrected entry: When Freddy and Janet arrive at Lawrence's mansion as his house guests, they arrive at night. Lawrence takes them upstairs and asks Janet to waltz with him in his ballroom. The scene takes place only a few minutes after their arrival. As they begin to dance, Freddy crawls to the door and starts moaning. Lawrence then shuts the ballroom door in his face and resumes dancing with Janet. As the shot cuts back to them dancing, a large window is plainly in view and daylight is streaming in brightly through the sheer curtains.
Correction: That is not sunlight. When they arrive, it is established that the house exterior is illuminated with artificial lighting. The light streaming through the window is not much brighter that the lamps in the room, which it would be if it was sunlight.
Corrected entry: When Freddie is telling Janet about his girlfriend and how she cheated on him, he indicated that the other man was "Danny" Terrio. (The former host of Dance Fever). His name is not Danny, it's Deney.
Correction: The people he's trying to con don't know this.
But the two sailors who volunteer to get rid of Laurence probably do it because they supposedly identify Freddy as a fellow sailor. I still think the army uniform was a mistake.