[BH] [AA] Owner charged when customers join spin class with hired instructor

When a business owner hires a Spin Class Instructor (NPC) and a customer joins the spinning class, the business is charged money for each customer instead of receiving payment. The fee for the class is deducted from the business owner's funds. The business should earn money from customer class fees, not lose money.

Expected Behavior:
When a customer joins a spinning class, the business owner should receive payment from the customer. The class fee should be added to the business funds. Hiring an instructor is a separate expense (class fee paid to the instructor), but customer payments should still go to the business.

Steps to Reproduce:

1. Own a business with the Businesses & Hobbies expansion pack.
2. Place a Gluteforce Instructor's Spinning Bike from Adventure Awaits on the lot.
3. Hire an NPC Spin Class Instructor.
4. Set a price for spinning classes.
5. Wait for a customer to join the class.
6. Check the business owner's funds before and after the customer joins.
7. Also check the business services after closing.

Actual Result:

• The business owner's funds decrease when a customer joins the class.
• The class fee appears to be charged to the owner instead of paid to them.
• This is the opposite of the intended money flow.
• Combined with the earlier bug where the owner is not paid when an instructor teaches, the financial outcome is doubly negative:
  • Owner receives no customer payment, AND
  • Owner is charged for each customer joining.

Additional Notes:

• This appears to be a sign error in the code — a plus/minus value is inverted.
• May be related to the broader spinning class payment bugs:
  • Owner not paid for classes taught by instructor/employee
  • Instructor leaving early
  • Owner forced to participate
• The bug essentially makes offering spin classes with a hired instructor a financial penalty per customer, which is completely backward.

Impact:
Game-breaking for fitness businesses. Offering spin classes with a hired instructor actively drains the owner's funds with every customer who joins. Combined with the "owner not paid" bug, there is no scenario where hiring an instructor for spin classes is financially viable. Players cannot run a profitable spin class business unless they teach every class personally and ignore the hired instructor feature entirely.