To be honest its all by chance regardless, if you buy with coins or if it drops out of thin air as a loot item. However, that being said it makes the game more enjoyable to be surprised to receive an exotic weapon that you have spent hours raiding for or pvp ing for. So I choose you crazy Bungie game of chance. Xur your just a sad imitation of my hard spent hours killing vecs and shooting ten year olds in crucible.