Unexplained "discount" given to buyer

[iamonourside]

I am the seller on an order. How can I find why and how a "discount" was applied to the order?

The order details shows a "discount" of $4.10, exactly offsetting the shipping charge of $4.10, as follows:

Item subtotal $115
Shipping 4.10
Sales tax (eBay collected) 8.63 (N. Carolina)
Discount -4.10
Total paid by buyer $123.63

I have confirmed through all other payment and order related eBay documents that the discount was in fact applied (more below).  But cannot found any documents to substantiate how or why the discount was given.  This sale followed from accepting an offer on an item with a shipping charge of $4.10.  I double checked the offer did not entail anything to do with shipping.  There are no messages either sent to or received from the buyer. There is no confirming email from eBay saying I'd sent an invoice.

Where can I find the invoice from which the buyer paid? Anyone suggest other places to look for history of the sale?

All documents shows the same discount and amount buyer paid, until I went to cancel the sale (because the item sold was delivered and then returned via "return to sender," members on the shipping board advised me to cancel the sale).  The cancellation details showed a different item price and an amount for buying payment of shipping costs, as below:

Total refund to buyer$115.00
Refund summary
Purchase price$111.04
Original shipping$3.96
Variable percentage$15.52
Refund amount you owe$99.48

I hesitated, and in the meantime the buyer filed an INR. She denies that she or anyone else received the item or initiated the return to sender. 

[donsdetour]

best guess is that you refunded them the shipping by the order details...

As for the INR put in the tracking: it shows it was not picked up by the purchaser and returned to you.