This is the first I have heard that drones are getting activated before being sold and that too, sold as new. An activated drone is considered second hand and not new anymore. It will NOT show up on the second purchases account.
Warranty will only be valid in the country of purchase. For any warranty claims, it would need other be sent to the Dji centre where it was purchased. I am in New Zealand and if I buy from Aussie, I cannot claim warranty here but need to ship it...