1 - People buying a handful of phones and comparing them, then returning all but the one they decide to keep.
2 - Semi related, one of the ten thousand phone comparison Youtuber channels.
I don't really know what the solution is. I think a phone rental business could spring up. Charge $10/day or something to rent a high end phone to folks to see how they like it.
My guess is that Bestbuy has more money so they can afford the rare demo phone getting stolen somehow. Funnily enough when I worked at Radioshack we often had people steal the fake phones that just played a video loop. Someone even tried to return a fake phone once saying that we sold them a broken device.
Think of it - if you are spending $1200 on an item, would you want to save $20 on it to get one that who knows who had for who knows how long? I sure wouldn't. You'd probably need to go at least $100 lower before it becomes somewhat appealing.