If a bidder doesn't pay for an invoice and you turn off their bidding privileges, it is prudent to check the 'Activity' tab in their Bidder Profile (Users page: Bidder Profile).

The Activity tab will list out each current auction the bidder has winning bids in. There is a 3dot Actions menu that has an option to 'Delete Winning Bids'. This will remove the bidders current winning bids and/or current max bids.

This action must be done for each auction, 1 at a time.