With something like that, there's not a whole lot of distinction between new and used. Also, Amazon tends to be pretty consumer friendly, so if there's an issue they'll likely have your back getting some kind of return processed.
Not sure if this is in the right spot. Sorry.
Is it wise to buy a used modem? I can get a used sb6141 off amazon used for $66 shipped. Or spend $86 on a new one. They have a 30 day money back guarantee also, if i need to return it.