I think that you ship only to India but an International Buyer has paid you less amount on shipping.
You have already conveyed her the same.
Now either you receive the balance amount through PayPal (or some suitable other means) or ask your buyer to agree for mutual cancellation of the deal and refund the money.
Your Buyer can then buy again at the agreed amount.
Someone from ebay may clarify if there is any other option available.
Umang Midha
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http://stores.ebay.in/IndConcepts
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best regards
Umang Midha