I suspect some lawyers will be employed to get a ruling on what is "fair." There are plenty of questions. Is "fair"the interest you get on a savings account, the inflation rate, or what the owners of the biggest apartment building in town  tell the city council? Do you use ROI or Cap rate (i.e. does it matter if you have a mortgage).  Does the city review the financial records of every landlord in town? If so, who is paying for these audits?