"That's fair," he says. "Do you currently use magic to preserve the scrolls? If not, it may be possible. I would be willing to make the attempt at such a spell." This isn't a lie. As a Witch, he's motivated toward learning new spells, no matter their nature. And something like this could be useful.

"I understand if you'd prefer not to have an outsider among your oldest scrolls. However, I am interested in learning more about your city, if only you'd allow it. Knowledge must always be cherished and protected."