Dedicated, preplanned rental can be done much more cheaply from conventional car-rental places. If you're on a business trip your business probably has a deal in place with one of the big companies, and you probably want to just have a car for the whole trip and not worry about it - especially since you're going to be expensing it anyway, and neither you or the expenses department wants the trouble of figuring out exactly how many hours of car rental is reasonable. Zipcar's great advantage is for unplanned, one-or-two-hour rentals (often because you need to transport something bulky, which a business would have specialist ways of doing), which is far more common for private individuals than businesspeople.