When hiring a company to refinish your hardwood floor always ask if they have dustless system, the price will be about a dollar increase for that service if you want to save some bucks you may get a service that does not have the dustless, but keep in mind, all big machines used for sanding have a bag that collects the dust and before staining or applying polyurethane all area should be completely free of dust to make sure of that the crew will blow the dust from the walls and vacuum  through.

While getting a company with a dustless system will be of course better because the dust will be less not 100% remember that sanding is a messy job and is not guaranteed that there will be no dust at all. Try to get different prices and compare the pros and cons considering your budget. If you or your family won't be in the property  and the crew will clover the air ducts it won’t really matter.