"The idea of charging to Dhamma teaching is quite at odds with the early Buddhist tradition. In the Udana the Buddha said: "One should not go about making a business out of the Dhamma"
"I don't think it is necessarily wrong to make money from teaching Buddhism, as long as one does so in an ethical manner. But money often tends to corrupt, and it is difficult to teach with the purest of intentions if you know that your livelihood depends on people paying you. In AN 4:50 the Buddha says that accepting money is a stain on ascetics and monks. (The text says gold and silver, which includes money in the idiom of the time.) At SN 42:11 the Buddha says that by accepting money you also consent to sensual pleasures."
"A true friend is a giver and not a taker. When there's money involved, there's expectation of what should be taught, and if that doesn't please the ego of the student, and most likely it doesn't, because that's the ill brought to the table, the so called student cannot but have a feeling that "I want my money back!"