You can believe us or go on line and read it for yourself. Those guys lied to you in order to take your money. Suggest you google Ohio Building code chimney or just go directly to Chapter 4101:2-8 Chimneys and vents - Ohio Revised Code
It's some real snoozy reading but you'll find the section 801.18.1 through 801.18.4 to be exactly germane to your application.
I would mark those guys right out of the book.