But this problem is exactly why we invented money in the first place... If I'm an interventional radiologist and I want to learn algebraic topology, what are th

But this problem is exactly why we invented money in the first place... If I'm an interventional radiologist and I want to learn algebraic topology, what are the chances of a coincidence of wants? How many algebraic topologists do you think there are in the world who will trade their time for a chance to get better at placing arterial stents? On the other hand, I can basically guarantee you that someone somewhere is willing to pay money for an arterial stent, and somewhere else there is a world-class expert mathematician who will accept money in exchange for tutoring.