This little pictographic interaction says it all. You can learn a lot from the generosity of others.
The "masters" of martial arts are at root masters because they will teach anyone with a strong desire to learn and martial arts is a about a lifestyle and not just a combat or defensive tool.
They will show you something that will blow your mind and as you think, i cannot ever pay the amount of money it will take to learn this, the master will say : "So you want to learn? Cone let me teach you!" Not thinking of profit or money but about the transfer of knowledge and skill.
Anyone who shows such characteristics, to me at least, is a master!