I worked at a retail store and the samsung reps left them for us when they added the newest device on the display so it kind of landed on my hands.
I agree, I too worked in a Samsung Store. They just leave them, or ask us to scrap them when the life cycle is completed as many are by then AMOLED burnt or battery dead. Sometimes, They bring extra and handover to us for promos and stuff.
The speed some people here on XDA jump to conclusion that it's stolen is crazy!