Then you can run reports per outlet. You can also apply user permissions on Customer so that cashiers can only see their outlet.
Now, if you need actual customers, I don’t believe there is an out of the box way to do this. You would need to create a custom field (outlet), write a script that fills this field in POS, and then write reports off this field.
Sales Invoice currently does not have a Warehouse field. However, it’s not as simple as just adding a custom field to warehouse because there’s currently no easy way to have that filled in POS.
Basically, if you cant go with generic customers, you’ll have to customize.