When I complete a job for a client I also make sure to let them know about our other services, I don't force anything on them, but if I see something like a wire running across the floor to a TV I make sure to mention we also offer wiring services.
I have found this works great in the past, along with leaving a business card which list your services on it.
I have found this works great in the past, along with leaving a business card which list your services on it.