I signed up with Cox Internet 2 months ago and installed an ARRIS modem compatible with Cox. So far, so good. I then needed to find a modem/router to add wi-fi. So I bought a used ARRIS modem/router compatible with Cox and had a Cox technician attempt to install it. It didn't work. So I assumed it was a bad modem. I then purchased another Cox-compatible modem/router(a used ARRIS product) and had a Cox technician attempt to install THAT one, Same result. So I'm wondering, first, whether it's common for used modems to not work? Or just to pay 4x the cost and buy a new one? Or is there another reason and another solution? BTW, my initial ARRIS modem was used and it works fine.