Which feature can be used to restrict users from a business unit from accessing the master customer list?

Many applications are used to try to get customers to either buy products, buy subscriptions or use their service free of charge. The application may seem like they are not making money if the service is provided free of charge, but they are because they are being paid by advertisements due to the large number of people using their application.

Northern Trail Outfitters is an application and it includes different platforms and frameworks like Lightning Component Framework and the popular Salesforce Platform. Even though it is associated with Salesforce and other platforms, the Northern Trail Outfitters pretends to be a clothing company that specializes in outdoor attire, but it actually relates to other companies that specialize in clothing. They may send promotional offers.