It depends on the context and where you are in the return.  Usually "services" and "sales" are different categories: 

• Services would include the charges for the time of the doctors, nurses, technicians who worked on the patient.
• Sales would include the cost of bandages, crutches, medicines, etc.

If this does not answer your question, please respond in this thread with additional information.

You said " WE are a medical clinic"  ... what form are you trying to fill in ?   A partnership or corporation ?   And who is WE  ?