Buffy shouldn't charge for saving people from demons but she could've absolutely charged for doing odd jobs in the supernatural community. Anya not once shoving Buffy at a demon who needed some benign task done that a slayer would be super qualified for feels like a missed opportunity.
Some demon child needs a nanny. A witch needs specific materials fetched from a super dangerous corner of town. This demon owes another demon money and is trying to skip dimensions to get out of it. Buffy accidentally becoming a fixer in town for the magically inclined. She never does anything she finds morally bankrupt for money but does get a reputation for being extremely reliable once she agrees to a deal. Her house and all debt is paid for in a month. She actually does discover a brewing apocolypse because a demon who needed yard work assistance once heard something from somebody else who saw something hinky going down in a factory last week.
