From the point of view of Jupiter boss, he is losing 600 baht (drink price in December) every time a customer goes to bar and only pay off fee for boy. If many customers did that, he would lose money. Not entirely wrong of him to recoup 1/3 of the money.
Something similar happened at Freshboys. A popular boy who performs in the show contacted mamasan to say he had a customer off him for the night through Line. He told mamasan that he would go to bar and pay 500 baht off fee then he would meet customer. Boss said no. Boss insisted that customer come to the bar, buy a drink and off boy. The boy was furious and quit. Currently working at Dreamboys and happy there.
Subsequently, the boss of Freshboys dropped insistence on customer going to bar to buy drink before offing boys. Now boys just have to pay 500 baht to bar per night if they don't report to work. No questions asked.