Use an estimate to explore likely cost
When quantities, access or the scope remain uncertain, explain the assumptions behind the estimate. A range in your notes can be more honest than an unexplained exact number, but the line-item total still needs a clear basis.
Use a quote for a defined offer
Set out the deliverables, quantities, price, validity period and exclusions. Describe how additional work would be agreed. The title alone does not determine legal effect; the actual terms and applicable law matter.
Example: a repair job
Before inspection, labor and parts may be estimated. After inspection, a quote can identify the required repair, specific parts and agreed price. If another fault is found, get agreement for the change rather than silently increasing the bill.
Keep the accepted version
Save a version and export a copy before changing scope. When preparing the invoice, reference the accepted document and review payment terms instead of carrying over an offer-expiry date.