Kind of what I was trying to say earlier. And materials not yet installed are not a part of real estate yet. Once you fasten it, bury it, etc. it becomes a part of the real estate.
If you are selling a service, say maybe security system, phone, internet, even fire alarm you can disable link to outside world, disable software, change access codes, or otherwise interrupt the service being provided. Unfortunately most of us here just install electrical items but don't sell the electrical service, internet service, etc.
You could sell and install PLC and wiring and have PLC linked via internet so you have remote access to help remotely service/update software type issues. Failure to pay, you could easily remotely disable that software and when customer complains it doesn't work tell them you will be happy to fix it once you are paid what is still owed to you, but you can't just go in and physically remove what is now a part of their property.