Getting a required business license to open a business in Tucson (and paying ensuing taxes) can be done online through the City of Tucson's Finance Department.
One thing to remember if you are buying an existing business is that you are liable for any unpaid taxes of the seller. Before purchasing any business, you should require the seller to provide a “Letter of Good Standing” issued by the City’s License Section, which is a document that states there is no tax amount outstanding.
If you prefer, you can also get a business license in person on the first floor of City Hall, 255 W. Alameda St. If you have any questions about starting a business, please call the City of Tucson's Small Business Assistance Line, (520) 837-4100 or email email@example.com.