The swiss flag waved by Franklin in the last scene is rectangular. The actual flag is square.
Burt wouldn't have been able to obtain a search warrant with what he found when he illegally entered Franklin's apartment. A warrant would be issued pretty quickly after Franklin's fingerprints were found everywhere, though.
When Franklin is trying to decide what to do with Mr. Olivetti's body, you can see Mr.Olivetti (who is supposed to be dead) blinking.
When Franklin crashes into the trash cans with the Pinto and backs up, the whine of a manual transmission in reverse is heard. Later it is revealed that he cannot operate a manual transmission.