>that seems a little naive. what about actual evidence of performing said wipe? a little progress bar showing the 35× overwrite technique maybe, verified by a failed recovery

Implementing this is problematic because depending on the filesystem, it might not be possible to "wipe" a file by repeatedly writing over it. For instance, if it's a log structured filesystem. On the other hand, you might not even need to overwrite in some cases, eg. filesystems on SSDs with trim support. Also you don't need 35x overwrites. There's no evidence that even 1x overwrite can be recovered on contemporary hard drives.