Paypal dispute case

I tried to reduce the shipping cost. So I only charge $3 for the shipping.
The registered letter to china would cost $12. This person didn't ask
register mail and didn't pay the registered shipping also.
Now this person in China said he didn't receive the item and wanted refund.
I scanned my receipt to PayPal. Is it good enough?
What should I do to win this case?
Thanks