I don’t believe verified businesses should have properties in the sewers. However I do believe property should be obtainable via purchasing through KimiNoUso depending on the business’ needs and what they’re about. For example, a car cleaning/maintenance business could potentially purchase the auto shop or old garage as their base of operations.
That also being said, do not forget that there is a tower dedicated to verified businesses for their “base of operations” as well. You would probably have to have a REALLY good example or reason as to why you’d want to expand outside your current office space.