After the first assassination, Viktor appears in an alley. He dumps the pizza carrier, switches jackets, and pulls his backpack up on to his shoulder. In the very next scene, as he is getting on to the bus, he is wearing a different hat, and the backpack is gone.
No shell cases are ejected ever during the movie.
In several scenes where people are driving in Romania, the wheel is on the right - signifying left-hand driving. However, Romania's driving is done on the right.
The Olympic revolver shown wouldn't actually fire. It is missing the pin that connects to the hammer (as seen several times).
In the dealing scene (empty white room) some lights can be seen near the wall installed on a tripod. After the shootout the lights are gone.
Why would Viktor have left the film-maker's ankle gun in place? Or if he did (to give the film-maker a false sense of security) he'd have removed the rounds from the magazine.
More than once Viktor is supposed to be loading his gun but is really putting an empty magazine in and racking the slide, leaving the slide in the open position. The slide will not close on an empty magazine. No hitman, or any other gunman, would do such a thing.