There are a number of 'home automation protocols' out there.
I spoke with a guy a few years ago, he had a bunch of "X10" equipment in his house - that uses the power wiring to send signals. That seems like a solid choice here, but Im not sure if any 'site prep' is needed (do they need a full time admin computer, on the X10 network ? or can you setup a switch to switch 2 outlets and walk away ?)
Zigbee and Z-wave are other bigger names in home automation. The reason I looked this way is because once you have a few pieces of home automation, its easier to be swayed into buying more, and automating more lights, garage doors, security system, timers on lights...and then all of a sudden you are in a sci-fi movie...wait...wut ?
I now know a number of people with wifi thermostats - they have no compliants- however every wifi thermostat has 'local' controls in case wifi gets lost or their wife gets too hot in the afternoon...
Lastly - Google Home/Amazon Alexa - Most 'smart speakers will work with some flavor of 'smart home devices', and they make 'smart light bulbs' now - so if the customer had an 'Alexa' or google home device, it can be paired to a smart light bulb, and then they use the smart speaker to turn the lights on and off. If they already have a smart speaker, this is the easiest to implement.
Sorry I have no direct experience - I am an EE and love reading/geeking about this stuff. If I had more time and money I'd probably have automated my home by now with something (but Googlezon speakers are too much intrusion for me...)
-John