Some TVs constantly display nag screens or blink the power LED at you if you keep them offline.

I can't decide if it's better to check for such things before purchase, or just return it as defective if I end up getting a model that does this.

Absolutely return as defective. Make it sting a little.

If it doesn't say on the box "requires constant internet to function" in big bold letters, it should.

What about saying in big bold letters 'requires constant electricity to function'?

That would be a ridiculous requirement, because people expect that TVs need electricity. But the producer can argue that people these days also expect TVs to need the internet, can't they?

They sure as fuck cannot, I've never connected a single TV to the internet. That's something that needs to be explicitly declared.

That would be a for a judge to decide.

They're going to take me to court for returning a TV?

They might refuse to accept your return, and you might have to enlist the help of the legal system, if you want to force them to accept it. Of course, details depend on your jurisdiction and on the retailer / manufacturer and what warranties they give you (or are forced to give you), etc.

I also use an AppleTV with my Samsung TV. I did give the tv WiFi credentials so that sometimes if needed it can reach the internet (eg firwmare download), but I set up firewall rules to block all traffic for the tv in steady state.

This is why i bought a Sony. They have a ton of features packed in but won't scream if you don't ever connect them.

> [...] blink the power LED [...]

You can fix that with a piece of tap or blu-tack.