Sims will be drawn to whatever space has the objects for what is set as the business activity. So my Sim runs a cafe & pottery store on the first floor of the family’s business, and his wife runs music classes on the second floor. The whiteboard and instruments are all upstairs, so while that business is open, customers generally go upstairs and don’t spend too much time downstairs. The cafe bar, tables, food display, and pottery sale shelves are all downstairs, so when that business is open customers rarely go upstairs and don’t generally stay long if they do.