I use faxzero.com, too, when I have to fax something to somebody who, for example, doesn't have a work e-mail address that can be used by the public. I've never run across having to do this in mystery shopping, but some government agencies still require faxed documents.
Highly recommend this. It's free for up to three pages, and I think it's something like $1.99 if you want to fax more pages, priority delivery, and/or want to remove the faxzero branding.
I learn something new every day, but not everyday!
I've learned to never trust spell-check or my phone's auto-fill feature.