Here is how to export just the winning bidder information for a sale, including the winner's username and the highest bid:
You can export your auction in any state (e.g. live, closed, draft, etc.). It may be most useful to do so when the auction has ended in order to retrieve winning bidder data.
Log into the admin site
Go to Auctions & Items > View Auctions
Locate your auction in the list. If you cannot see it, check the Modify Filter settings
Click the Export button in the Actions column.