Build an estimate someone else can check
Use clear item descriptions, quantities and pricing units. Separate optional work from the main scope and make exclusions easy to find. Check tax treatment and currency with your finance process rather than relying on a copied previous document. A colleague reviewing the estimate should be able to understand how the total was reached and which customer requirements it covers. Record the validity period and the next step for approval.
Keep changes visible through acceptance
If the work changes, update the estimate deliberately and explain the difference to the customer. Agree who can approve discounts or altered terms before the document is issued. An accepted estimate can support the next billing step, but the team should still review the final customer details and payment schedule. For work delivered in phases, decide whether separate estimates or a staged invoicing arrangement makes the commercial position easier to follow.