I would always tell my customers that I guarantee my installations for life: During either my lifetime or theirs (whicever ends first), I will replace any worn out wiring or devices free of charge (not including faceplates, fixtures or appliances). Invariably, there would be more work they needed, while I was there, that made it profitable for me to give away a couple of switches or receptacles. They always loved it when I would say, "All done, no charge." I always loved it when they would say, "While you are here, could you...."
