If your entire marketing system is a Facebook page and a private group, you do not have much of a system.
You have a channel.
Channels are useful. But businesses should not confuse a social-media audience with a customer database, searchable marketplace or owned marketing platform.
A stronger system can let a business manage its own profile, publish inventory, post events, issue promotions, generate QR codes, capture leads and measure traffic without depending entirely on one social network.
It also means the business can be discovered by people who are not already following the same local pages.
If every promotion reaches the same people, your audience may be active without actually growing.
Social media should feed the system.
It should not be the entire system.