The rates on fixed price and hourly price jobs do not include the cost of spare parts or additional work (for partnership jobs) required. If you need to add extra costs, you can use the 'Additional Payments' feauture in the App, available after the job has been started. When you request an Additional Payment the customer will get a text message to approve the payment. Ensure to discuss the payment with the customer in advance, and that you have received approval from them (you will get a notification once that's done) before doing any additional work. You can also transact with the customer directly on additional payments.