Either. Some people farm battle tower every day in order to get points/items. You can buy/sell on Playerdex mart website, in-game, or if you can't find what you want, make a post in the Trade channel of PWO's Discord server. An item that costs 300BP usually goes for 250-300k Pd. The easiest method for battle tower is to unlock Custom Battle and all possible Daily Goes (up to 8) which yields 50BP per day, about 15 minutes work slaying Magikarps. Takes a while to unlock that much earning potential.