They may not know how much the slop is, or the exact procedure to open it if you do know the combination (turn left X times, then turn right Y times...). Though

They may not know how much the slop is, or the exact procedure to open it if you do know the combination (turn left X times, then turn right Y times...). Though you'd expect a locksmith with access to a safe-cracking robot would also have access to documentation showing that. Or as others said, the lock mechanism could be faulty or seized.