they already have audio video surveillance signs posted everywhere from the moment you walk in so that would go over like a lead balloon

They have video surveillance signs. Audio is a different category in a lot of states. In California, it's illegal to record audio without consent of all of the parties, and I believe you can get a civil remedy of $5000 for this.

I would be willing to bet the TV's demo mode used by most box box retailers disables that by default, specifically to avoid such an issue.

Someone needs to find out. Presumably by the TOS it's in the settings, so verifiable

Finding out would no doubt involves a violation of the CFAA or anti-circumvention or other measures imposed by the corpos.

Ask them if the TVs come with the necessary and relevant audio surveillance signs.