'Sold Books' records will not be deleted if they are part of a 'Catalog'. The 'Catalog' must be deleted. Deleting a catalog will not delete available items listed in the catalog.
For more information on deleting a catalog read the article:
1) On the admin dashboard page, scroll down to the heading 'Inventory Snapshot' on the right of the page.
2) 'Select a purge time' from the drop-down menu. This will determine how often your sold records are deleted.
3) Check the box next to 'Automatically purge sold inventory ____'.
4) A pop up window will appear asking you to confirm, Click the 'OK' button.