Comcast XFINITY → Re: Check Your Comcast Bill- Modem Rental Fees

Make them produce the install paperwork with the model and serial number of the unit. It must also bear your signature, acknowledging their having installed, and your agreeing to pay to replace their equipment if it's damaged, destroyed, or lost. They always make you sign when they've been there, and they put down those details so there's no switcheroo action.

I don't believe I've EVER signed anything when they've been here.

I'm OCD when it comes to boxes and receipts for electronics and other big purchases. I have a closet full of original boxes with the receipts in or attached.

I had to sign every time they came out to fix problems with reception or the STB. I dumped them back in 2009 so I don't know what their practices are these days...though several folks I know in Maryland were even asked for ID when their boxes had to be replaced.