"The - aboveboard - ways of doing it involve media recommendations, commissions for pieces of music or art, or live performances of same. This only gets you so far. And eventually someone hit on the idea that if there were daeva worlds and us maybe there were more than those, and they figured out a way to summon demons from other worlds. Demons who you could trade all our world's media, because they'd heard of none of it, demons who you could trade technology if they were from a world that was not as advanced as ours.
A while ago I needed a fleet of starships. I did not have anything on hand with which to pay for such a thing. I summoned a demon from a world that had not yet mastered travel faster than light, and I offered to trade her the knowledge for the ships, and she accepted - well, asked me to grab her twin sister as well, actually, her twin sister was an angel and they didn't get to see each other very often -"