Ah, yes, forgot about that. Well, do magical girls have a salary? Or is it with those coupons they receive when the commit genocide?
Magical girls collect stamps to get any wish fulfilled. And it does not require genocide. The goal of the Light clan is to make Dark Clan "unable to affect the world" aka seal them. Killing Dark Clan members is only a last resort, although how a magical girl goes about their hunts is up to them. They have a shocking level of autonomy. So there might indeed be magical girls who indiscriminately slaughter any Dark clan member they find.
It does not seem like magical girls get money unless that's what their "wish" entails after finishing a stamp card. Sakura might have made some money by saving people or completing a task, maybe she was already rich to begin with, who knows? She has definitely invested in real estate in this town she protects and owns like half the area. Momo seems to have no interest in any of that though, so she probably doesn't investigate.