Not to be facetious (but on cue with your pushback expectation), when you buy a car do you ask the reseller/dealer to itemize the cost for tires, transmission, catalytic converter, flux capacitor, etc.?? Don't most people feel like they're making an informed purchase when buying a vehicle??
When an integrator provides an itemized list of REAL part numbers with cutsheets and a site diagram and/or line diagram, he/she is taking responsibility for the system as a whole. Referrences and/or job locations are probably better questions to verify that he/she is a trusted integrator and that they stand behind their systems.
Itemized pricing only leads to bid shopping which has happened to me personally in private and public sector jobs. And if that is a sticking point, I'd rather lose the job than do the homework for the buyer/project manager to take my design and hand it to his buddy to install and get a kick back on the side ... which I know NEVER happens anywhere ever.