"Sweet talk" may be a little high in the expectations dept, but you can gain favor by being 110% prepared and ready to speak thier language when you meet. Your fire marshal is right- it is a public assembly, and our process ended up as our haunt being coded like a museum- public assembly with no seating.
I was polite and respectful when we met more than a half dozen times to exchange information- and I always returned with the answers to their questions. Our building is zoned light industrial, but gained approval for its use as a public assembly without a zoning change.
Make sure to ask for approvals in writing.