A salesman's job is to get you to not walk out of the store without buying something. What they have, right there and then, is what you need. I'd be curious if that Denon AVR was a model that was made for Best Buy retailers only. That does happen all too often. I have no way of knowing if that was the case here, but it would not surprise me.
A few year back, I was in the market for a new TV. During my research I found that certain Vizio model numbers were only made for Best Buy retailers, and to avoid those models if you were looking at used Vizio TVs.
Let the buyer beware.