I'm sorry to hear that you received an unsolicited payment. To best protect yourself, if someone sends you a payment that is not expected, you can refund the payment using the issue refund link. The payment will go back to the source, in the currency that they originally used. Never send a separate payment for a refund if it can be avoided.
Thank you also for reporting the situation. PayPal will not respond with any details about an investigation or action regarding another PayPal member.
I hope this helps!
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