I think if I were taking a class, I might feel obligated to buy something there. As Sheri.a said, the instructor gets the money for the class.....or probably the biggest part of it, and the shop owner provides the space, probably in hopes the pupils will buy enough to pay for the electricity and such.
I haven't ever taken a class. I wouldn't know how to act in one, lol. But really, I think I might be impatient if the instructor droned on and on. Or get frustrated if she went too fast.