I'm a little a head so I'm giving the olam time to get ready to see this when the time comes
The gemarah says that you shouldn't teach torah for pay even when you learnt for pay. the gemarah gives a Pasuk that ends with "you shouldn't sell it". It would seem to say if you teach for pay you're selling your torah.
The gemarah in the begining of A"Z says that when you learn you acquire the torah to be yours. In kidushen says that a rebbe could be mochel his kovod because it's his torah. therefore, if he teaches for pay he sold his right to his torah that he taught him. The kovod of a talmud to a rebbe is partly for it's his torah that's in him, but by selling it he lost the claim that his torah is in him
maybe this is a makor to the sefer chasidim brought in rama yd 242-34 that when the father pays the rebbe (shach-or anyone else who pays)he gets the privilege to get his aveida reterned first over the rebbe's

This message has been edited. Last edited by: Rav Chaim,