Trading in things that come with a prescription (medical devices included) is a fast ticket to a fine the site might go bankrupt under or
lawsuits if they were the conduit through which a counterfeit product was sold.
"It is illegal to sell, give away, or trade prescription drugs and medical devices over the Internet or through other means of advertising or private distribution. Yes, people do it, but they are breaking the law."
citation: http://womeninbusiness.about.