This question has been debated for years, and there is no definitive answer. Some people believe that the machines are rigged in favor of the house, while others believe that they are not as rigged as people think.
There is no definitive proof either way.
Many experts believe that the machines are not rigged, but this is not to say that they are immune to systemic corruption. It is possible that certain casinos have deal with insiders who can help them alter the odds of the machine in their favor.
However, this is relatively rare, and it is more likely that individual dealers are manipulating the machine in their own favor rather than using a system to rig the game.