Srila Prabhupada once pointed out in a lecture that brahmanas (as teachers) used to work for free, that the relationship with their students was one of love. He said, “Just like in our institution, I am your teacher, but there is no such contract that you have to pay me. But you pay me more than anything.” (May 27, 1972, Los Angeles, Srimad Bhagavatam 7.5.22-34).
“Reciprocity perfected”