Service call plus additional labor
A service call fee covers the trip and the first hour. Anything beyond that is additional labor at an hourly rate, with the hours stated. Overtime, after-hours and holiday rates should be in the contract, not invented on the invoice. If the job is quoted as a fixed price, do not add hourly labor on top.
Parts and warranty
Itemize the parts — receptacles, breakers, wire, fixtures — with quantity and unit price. A small markup is normal, but disclose it in the quote or contract. State the warranty on parts and labor; a one-year warranty is a useful line on a commercial invoice.
Permits and inspections
A permit is a pass-through cost. If the inspection fails because of your work, the re-inspection fee is usually yours; if it fails because the customer changed the scope, bill it as an extra. Say which one applies.
Commercial clients and POs
Commercial customers often require a work order or PO number before the invoice can be paid. Put the number in the reference field, match the invoice to the work order, and send it to the AP contact — not just the site manager.
Tax and terms
Labor and materials can be taxed differently depending on the state. Net 15 is common for service work; Net 30 for property managers. If you charge a diagnostic fee that is credited against the repair, show that credit as a line, not as a discount the client has to infer.