The Online Scheduler feature within the ISN has a great feature for scheduling (or not scheduling) in zip codes that you designate as servicing.
First, you will need to set up your zip codes as described in this article.
Once the zip codes have been entered and designated as serviced or not, the next step will need to be completed to ensure scheduling via the Online Scheduler recognizes the zip codes the inspector works in.
Navigate to: Settings -- Office Settings -- Online Scheduler Settings -- Online Scheduler Settings
From the General Settings tab, scroll down to the following setting, and enable the setting by clicking the box.
Once that setting has been enabled (turned-on), scroll down to the bottom right-hand side of the screen to Save Settings.