Not sure the disconnect here. I wouldn't necessarily purchase a used card online, however purchasing directly from Navionics, it doesn't take much to do updates. Simply use a computer, install the Navionics update app from the site, put your card in and it detects the card and updates it. The only problem I've had is that their main tech support tends to be via email versus over chat or on the phone.
Jim,
not sure where you're located but I'd be glad to help troubleshoot if you're near me in NW Houston.

photofishin, I appreciate the offer; I'm up in New Caney. NW Houston is right around the corner, but I'm off on Mon / Tue rather than weekends. If you are free on one of those days, I can arrange a trip on a private, posted 85 acre lake full of bass and crappie south of Conroe, about 4 1/4 miles east of IH-45 (the owner is one of my fishing partners; he has let me bring guests before). You can show me how to work it (if it works at all) and catch a bunch of fish at the same time. Interested? I'll try to watch this site for a response (I've been internetless lately).
Jim