Their sacred text looks like words on a page the same as any number of other texts, some of which other people consider sacred, and some of which get considered blasphemous.

Whatever, dude, it's all just words on a page.

No such thing as a sacred text unless there must also be sacred ideals.

If they believe in sacred ideals, then ask them if every sacred ideal finds written expression within their sacred text.

If they tell you no, than you're probably dealing with a humanist, although they may not consider themselves as such.

Nevertheless, you can work with a humanist; they're not the type who will kill you over a slogan on your t-shirt or an editorial cartoon you may have drawn once, twice, three times a heretic. 

If they tell you yes, on the other hand, yes, ALL the sacred ideals can be found in the sacred text and no other sacred ideals exist besides those written down in the sacred text, then at least you know you're dealing with an irrational, mythologizing fundamentalist.

Skip to step 4.