I can't believe nobody has recommend a ducted vac (central vacuum in US). We sell them at my site. They are reliable and last on average for 10-15 years. And when they do break you just need a new vacuum motor, or to replace the filters. A much cheaper option in the long run for your own home. Obviously, not possible if you're running a cleaning company. That said, imagine how much you could save a prospective company if they were installed and you weren't passing on the costs of buying a new portable every few months.