I attempted to buy your Porsche for $20. You ignored me so I took it anyway.
Obviously it's illegal.
Obviously it's illegal.
The GP's example was bad because he mentioned taking a product or service, rather than making a copy of something and keeping it. I'm assuming he didn't mean it the way it reads.
Wrong. In your scenario, the DVD in question is for sale, and is clearly listed as such with a price and all. You know exactly how much it costs, and you give that much money. And the transaction occurs in a place that is designed for this very purpose. There is no confusion or grey area here.