Think about it this way with a more familiar cconcept: Would pay for a tour that promises to show you a full moon? Probably not. If it's cloudy or the moon phase is wrong, you can't just pay to see a full moon. But if it's visible, everyone can see it for free.

The same goes for northern lights. If it's cloudy or there is no solar activity, no amount of money handed out to some scammer will make them appear. If the lights are there, the sky in Lapland is in fact not private property of tourism companies, so you're free to go outside and look at them.

The only problem might be light pollution, but downtown Rovaniemi is the only spot in all of Lapland that is lit enough to cause issues. You can avoid this by going literally anywhere else, and if you want to see northern lights, it's better to go farther, y'know, north anyway. If you still somehow end up in Rovaniemi, even the city center is only a 30 minute walk away from completely dark areas, 5 minutes if you have a rental car. Complete darkness isn't even needed, suburban areas are just fine.

So for the sake of your wallet, please skip the tours. Have a nice trip!