requesting refund on accidental double purchase

[Beauty Bonetto]

i bought 2 piano's by mistake where do I find the payment history to show store owner?

[Lindal Kidd]

Look in Account/$L Transactions, on the left side of your Dashboard page.  Set the date range to include your piano purchase.  Highlight the details of the transaction, copy with CTRL+C, paste them into a note or IM with the store owner with CTRL+V.

The Transaction History only keeps data for the last 32 days.  If you bought the item longer ago than that, you may still be able to get purchase details if you bought it on the Marketplace.  If so, go to Shopping/Marketplace, select My Marketplace in the upper right corner, and click Marketplace History.

[Alwin Alcott]

as already in the other anwer is the right way to find the history, but a seller doesn't need to refund you. It's not his mistake.

If the item is transfer you will most likely not get a refund anyway.

[Innula Zenovka]

While the store owner is certainly not under any obligation to offer you a refund, my business partner and I would always offer one, since if the item is copy/no-transfer it's an obvious mistake and if the item is no-copy but transfer, then the customer can return the superfluous copy to us.

Certainly worth a try.