Setup a demo version of CMSB
I haven't used it for a while, but there is a 'demo' mode built into CMSB.
All you should have to do is to set up a separate install of CMSB with the setup and pages that you want in your demo site and after you've tested the new site, change 'demoMode' => '0', to 'demoMode' => '1', in settings.dat.
When a potential customer goes to the demo site and logs into it's CMSB, a separate temporary database is set up for them so that they can access the parts of the back end that you've allowed.
Note that in order to make any admin changes to your install you'll have too change the settings.dat entry back to 'demoMode' => '0',
There's more info at https://www.interactivetools.com/docs/cmsbuilder/demo_mode.php
Take advantage of a free 3 month trial subscription, only for CMSB users, at: http://www.thecmsbcookbook.com/trial.php