Question regarding French politics (possible spoilers)

Hi--

I was unable to do an Internet search for answers to these questions:

1. Is it a legitimately-sourced story that gangs canvass their neighborhoods to help politicians? Make promises of individual favors to gain votes? Or are these popular rumors started by political groups that don't do well in these areas?

2. Is it a legitimately-sourced story that gangs have actually blocks doors to polling stations by bricking them up or welding them shut? Or are these popular rumors started by political groups that don't do well in these areas?

Thanks for answers!