A:Answer You kinda answered your question. It's a marketing gimmick. There is not much else to think about it.
If you check on Amazon, there will sometimes be more expensive items listed at $400 originally $800 so you think you're getting a great deal, but when you check other places the prices are $400 originally.
Again, it's really just a marketing gimmick. The full-price drone is $900, so it could also be there so that people take a second look and realize they're buying a refurbished drone and not a new one for half the price.