Write from facts rather than momentum
Pause long enough to remove accusations, assumptions, and details that belong to someone else. For a message about how to dispute an incorrect mechanic bill, use this factual base: include the product or service, order number, dates, price, fault, prior contact, and supporting record.
Offer a proportionate next step
Match the size of the request to the relationship and to what the recipient can reasonably decide now. Request a specific lawful remedy and give a reasonable response date before formal escalation. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Protect privacy on both sides
Do not exaggerate, threaten staff, publish private details, or demand compensation unrelated to the loss. Use payment, regulator, insurance, police, data protection, or legal channels for fraud, danger, or unresolved rights. Use the most private legitimate channel available and do not share the exchange to recruit support or pressure.