I have typed up a form in the following matter.
I______________ residing at (address) have given permission to the installer (tech name or company name) to complete work for the installation of cabling and all necessary equipment that I requested. I acknowledge that I (customers name) as a tenant, assume all liability and responsibility for this installation. Whether a renter/leased tenant or a homeowner, I am aware that I have released the installer, service providing company and all of their affiliates from any and all liability. I have been fully advised and understand the installation process.
(Before starting the install)
Authorization to proceed. (customers name & date)
(after completion of install)
I am completely satisfied with my install (Customers name and date)
Not sure if it will hold up in court, never had to try, but it should cover you butt if needed. Get a witness signature also if possible.