@HeyImAlex Who are they going to call? Literally, I do not care. Consider: You bought a house. 6 months later the furnace failed. You’re going to call the previous owner and throw a fit? LOL no, you’re going to replace the furnace.
Homes require maintenance. This fact should come as a shock to no one (well, apparently no one except the people I bought this place from). EVERYTHING needs maintenance. Paint the outside, mow the lawn, replace the roof every so many years, replace the windows every so many years, replace the furnace filter monthly, keep the AC condenser (or evaporator? The part on the outside of the house, I’m not an HVAC guy LOL) clean, pressurewash the deck (it’s composite), keep the water softener full of salt, have the chimney cleaned once a year, etc etc. My stance is simply that the “smart house” portion of the house requires maintenance as well. It’s not rocket surgery.
And yes, it’s pretty easy to disable updates. Especially when everything is on a segmented IoT VLAN that you can just firewall off from the internet. No internet, no updates. Pretty simple. New owner changed something and it broke? That’s not my problem - it worked when they bought it.
As for the rest of your legal concerns, I’m not sure where you live, but homes don’t come with warranties from the seller in the US. Sure, there are legal remedies for things like “failure to disclose”, and structural deficiencies, etc. But the argument you make about “being the manufacturer”, etc - there’s simply no standing, nor precedent, for it.
The way that your argument begins to make sense is if you hung out a shingle as a “smart home installer”, and started putting HA and various equipment into people’s houses, and charged them to do so - in fact, selling them a “smart house” solution. Absolutely you’d have some liability for systems you installed.
The fact that the buyers of a house chose to buy a house that has pre-existing smart-home tech in it? Yeah, no.
@123 Of course it will be functional when it’s sold. OMG, I would be CRAZY pissed if stuff worked when I looked at the house and then didn’t work at closing - not to mention that in THAT case, there may be legal problems. I agree, there are different approaches to wording the sale, and for that, a realtor would definitely be involved. But to be clear (I know some of my previous posts have been lengthy, so they may have fallen into the category of tl;dr), my house is not presently for sale, I have no interest in selling, and barring an offer for twice (or greater) what I paid for it last year, I won’t be selling it any time soon. LOL The discussion is purely academic, and my initial reply was in response to what the actual value of a smart home is. Nothing more.
When the time comes that I do sell, rest assured, this will all be accounted for - including transfer of management accounts and how to change passwords on said accounts. Or, if the realtor recommends instead leaving instructions on how to create their own new accounts and link them to the gear that has then been factory-reset and the smart home features are “included but require configuration”, then that will be that. If they recommend taking it all out and taking it with me to the next house - then that’s what’ll happen.
I suspect that by the time comes when I do sell the house, there will have been a sufficient number of smart homes sold nationwide that there exists better, more professional (and legal?) advice on how to transfer that ownership. But again - for now, I have no interest in transferring or selling anything, and I honestly don’t care if it adds one wooden nickel to my current valuation. I like it, I own it, I live here - so I’m doing it. If along the way it happens that “the realtors on the internet” were right, and it added 15% to the value of my house, then great. If they were wrong? Small investment for many years of enjoyment, and one I certainly will not regret.
Thankfully it’s rather unlikely I’ll ever buy a house from you 
