[Doitsu]

Originally Posted by AlanHK

Ideally I was hoping for an unzipper that will work regardless of nominal filetype.

There's a free 7Zip clone for Macs that'll do the trick.

Tell your client to try the following:

1. Install and run Keka.
2. Select Preferences > General > Actions > Always extract.
3. Select Preferences > Extraction > Extract to location > Next to original file.
4. Close Keka.

Once these preferences have been selected you can unpack ePubs by right-clicking the ePub and selecting Open with > Other > Keka > Open.