I think that those machines are only sold by prescription so I don't think you can sell them. One of the sites I visited said, "Note - By federal law, in order to purchase a CPAP machine, BiPAP machine, Auto CPAP machine or heated humidifier a valid prescription from your physician that is less than one year old is required."
Perhaps you could dontate it to your local health department or visting nurses? They may know of a patient who needs one and can't afford it and you could maybe get a break on your income tax for your donation...
Just a thought.
"As one goes through life one learns if you don't paddle your own canoe you don't move."
"Madness takes its toll.
Please have exact change."