Start with the part that is verifiable
Separate the event you can describe from the motive or reaction you are guessing. For a message about how to ask a private seller for a refund, use this factual base: list the amount, date, reason, receipt, prior agreement, and any part that remains genuinely disputed.
Make one answerable request
Give the recipient one concrete question or next step instead of several emotional jobs at once. Propose a payment, refund, evidence exchange, or installment plan with dates both sides can assess. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Leave the recipient in control
Do not threaten public exposure, add invented fees, or treat hardship as proof of dishonesty. Use secure payment methods and qualified banking, consumer, legal, or fraud support when appropriate. A clear message remains useful even when the answer is no or no answer arrives.